diff --git a/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpec.groovy b/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpec.groovy
index 670beb5..ed0d4e3 100644
--- a/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpec.groovy
+++ b/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpec.groovy
@@ -1,13 +1,13 @@
 package com.jessebrault.ssg.buildscript
 
+import com.jessebrault.ssg.buildscript.delegates.BuildDelegate
 import groovy.transform.EqualsAndHashCode
 import groovy.transform.NullCheck
 import groovy.transform.PackageScope
 import groovy.transform.TupleConstructor
 
 @PackageScope
-@TupleConstructor(defaults = false)
-@NullCheck(includeGenerated = true)
+@NullCheck()
 @EqualsAndHashCode(excludes = 'buildClosure')
 final class BuildSpec {
 
@@ -29,6 +29,19 @@ final class BuildSpec {
     final BuildExtension extending
     final Closure<?> buildClosure
 
+    BuildSpec(
+            String name,
+            boolean isAbstract,
+            BuildExtension extending,
+            @DelegatesTo(value = BuildDelegate, strategy = Closure.DELEGATE_FIRST)
+            Closure<?> buildClosure
+    ) {
+        this.name = name
+        this.isAbstract = isAbstract
+        this.extending = extending
+        this.buildClosure = buildClosure
+    }
+
     @Override
     String toString() {
         "BuildSpec(name: ${ this.name }, isAbstract: ${ this.isAbstract }, extending: ${ this.extending })"
diff --git a/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtil.groovy b/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtil.groovy
index 309a148..a246e5f 100644
--- a/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtil.groovy
+++ b/api/src/main/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtil.groovy
@@ -57,7 +57,7 @@ final class BuildSpecUtil {
         }
         def allResults = mapBuildSpecsToResults(specs)
         def outputDirFunctionResult = reduceResults(allResults, OutputDirFunctions.DEFAULT_MONOID) { acc, r ->
-            r.getOutputDirFunctionResult(acc, { OutputDirFunctions.DEFAULT_MONOID.zero })
+            r.getOutputDirFunctionResult(acc, { acc })
         }
         def siteSpecResult = reduceResults(allResults, SiteSpec.DEFAULT_MONOID) { acc, r ->
             r.getSiteSpecResult(acc, true, SiteSpec.DEFAULT_MONOID)
@@ -77,7 +77,7 @@ final class BuildSpecUtil {
         }
 
         new Build(
-                specs[0].name,
+                specs.last().name,
                 outputDirFunctionResult,
                 siteSpecResult,
                 globalsResult,
diff --git a/api/src/test/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtilTests.groovy b/api/src/test/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtilTests.groovy
new file mode 100644
index 0000000..b870b72
--- /dev/null
+++ b/api/src/test/groovy/com/jessebrault/ssg/buildscript/BuildSpecUtilTests.groovy
@@ -0,0 +1,49 @@
+package com.jessebrault.ssg.buildscript
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.extension.ExtendWith
+import org.mockito.Mock
+import org.mockito.junit.jupiter.MockitoExtension
+
+import java.util.function.Function
+
+import static org.junit.jupiter.api.Assertions.assertEquals
+
+@ExtendWith(MockitoExtension)
+final class BuildSpecUtilTests {
+
+    @Test
+    void overwrittenOutputDir(@Mock Function<Build, OutputDir> spec1OutputDirFunction) {
+        def spec0 = new BuildSpec('spec0', true, BuildExtension.getEmpty(), {
+            outputDirFunction = { }
+        })
+        def spec1 = new BuildSpec('spec1', false, BuildExtension.get('spec0'), {
+            outputDirFunction = spec1OutputDirFunction
+        })
+        def r = BuildSpecUtil.getBuilds([spec0, spec1])
+        assertEquals(1, r.size())
+        def b0 = r[0]
+        assertEquals('spec1', b0.name)
+        assertEquals(spec1OutputDirFunction, b0.outputDirFunction)
+    }
+
+    @Test
+    void outputDirManualConcat() {
+        def spec0 = new BuildSpec('spec0', true, BuildExtension.getEmpty(), {
+            outputDirFunction = OutputDirFunctions.DEFAULT
+        })
+        def spec1 = new BuildSpec('spec1', false, BuildExtension.get('spec0'), {
+            outputDirFunction {
+                it.andThen {
+                    new OutputDir(new File(it.asFile(), 'spec1'))
+                }
+            }
+        })
+        def r = BuildSpecUtil.getBuilds([spec0, spec1])
+        assertEquals(1, r.size())
+        def b0 = r[0]
+        assertEquals('spec1', b0.name)
+        assertEquals('spec1/spec1', b0.outputDirFunction.apply(b0).asString())
+    }
+
+}
diff --git a/cli/src/main/groovy/com/jessebrault/ssg/AbstractBuildCommand.groovy b/cli/src/main/groovy/com/jessebrault/ssg/AbstractBuildCommand.groovy
index 332ebc2..98bcd08 100644
--- a/cli/src/main/groovy/com/jessebrault/ssg/AbstractBuildCommand.groovy
+++ b/cli/src/main/groovy/com/jessebrault/ssg/AbstractBuildCommand.groovy
@@ -1,6 +1,5 @@
 package com.jessebrault.ssg
 
-import com.jessebrault.ssg.buildscript.DefaultBuildScriptConfiguratorFactory
 import com.jessebrault.ssg.util.Diagnostic
 import org.apache.logging.log4j.LogManager
 import org.apache.logging.log4j.Logger
@@ -10,12 +9,6 @@ abstract class AbstractBuildCommand extends AbstractSubCommand {
 
     private static final Logger logger = LogManager.getLogger(AbstractBuildCommand)
 
-    @CommandLine.Option(
-            names = '--baseDir',
-            description = 'The base directory for all components.'
-    )
-    File baseDir = new File('.')
-
     @CommandLine.Option(
             names = ['-s', '--script', '--buildScript'],
             description = 'The build script file to execute, relative to the baseDir.'
@@ -50,12 +43,10 @@ abstract class AbstractBuildCommand extends AbstractSubCommand {
         logger.traceEntry('requestedBuild: {}', requestedBuild)
 
         if (this.staticSiteGenerator == null) {
-            this.staticSiteGenerator = new BuildScriptBasedStaticSiteGenerator(
-                    [new DefaultBuildScriptConfiguratorFactory(this.baseDir)],
-                    this.buildScript == new File('ssgBuilds.groovy') || this.buildScript.exists()
-                            ? new File(this.baseDir, this.buildScript.path)
-                            : null,
-                    this.buildSrcDirs.collect { new File(this.baseDir, it.path) },
+            this.staticSiteGenerator = new CliBasedStaticSiteGenerator(
+                    new File('.'),
+                    this.buildScript,
+                    this.buildSrcDirs,
                     this.scriptArgs
             )
         }
diff --git a/cli/src/main/groovy/com/jessebrault/ssg/CliBasedStaticSiteGenerator.groovy b/cli/src/main/groovy/com/jessebrault/ssg/CliBasedStaticSiteGenerator.groovy
new file mode 100644
index 0000000..1395b9a
--- /dev/null
+++ b/cli/src/main/groovy/com/jessebrault/ssg/CliBasedStaticSiteGenerator.groovy
@@ -0,0 +1,47 @@
+package com.jessebrault.ssg
+
+import com.jessebrault.ssg.buildscript.DefaultBuildScriptConfiguratorFactory
+import com.jessebrault.ssg.util.Diagnostic
+import groovy.transform.PackageScope
+
+import java.util.function.Consumer
+
+@PackageScope
+final class CliBasedStaticSiteGenerator implements StaticSiteGenerator {
+
+    private final File baseDir
+    private final File buildScript
+    private final Collection<File> buildSrcDirs
+    private final Map<String, String> scriptArgs
+
+    private StaticSiteGenerator staticSiteGenerator
+
+    CliBasedStaticSiteGenerator(
+            File baseDir,
+            File buildScript,
+            Collection<File> buildSrcDirs,
+            Map<String, String> scriptArgs
+    ) {
+        this.baseDir = baseDir
+        this.buildScript = buildScript
+        this.buildSrcDirs = buildSrcDirs
+        this.scriptArgs = scriptArgs
+    }
+
+    @Override
+    boolean doBuild(String buildName, Consumer<Collection<Diagnostic>> diagnosticsConsumer) {
+        if (this.staticSiteGenerator == null) {
+            this.staticSiteGenerator = new BuildScriptBasedStaticSiteGenerator(
+                    [new DefaultBuildScriptConfiguratorFactory(this.baseDir)],
+                    this.buildScript == new File('ssgBuilds.groovy') || this.buildScript.exists()
+                            ? new File(this.baseDir, this.buildScript.path)
+                            : null,
+                    this.buildSrcDirs.collect { new File(this.baseDir, it.path) },
+                    this.scriptArgs
+            )
+        }
+
+        this.staticSiteGenerator.doBuild(buildName, diagnosticsConsumer)
+    }
+
+}
diff --git a/cli/src/main/resources/ssgBuilds.groovy b/cli/src/main/resources/ssgBuilds.groovy
index 9221535..04592bd 100644
--- a/cli/src/main/resources/ssgBuilds.groovy
+++ b/cli/src/main/resources/ssgBuilds.groovy
@@ -4,26 +4,19 @@ import groovy.transform.BaseScript
 import com.jessebrault.ssg.buildscript.BuildScriptBase
 
 @BaseScript
-BuildScriptBase base
+BuildScriptBase b
 
-allBuilds {
+abstractBuild(name: 'mySiteAll', extending: 'default') {
     siteSpec {
         name = 'My Site'
-    }
-
-    globals {
-        greeting = 'Hello from AllBuilds!'
+        baseUrl = 'https://mysite.com'
     }
 }
 
-build('production') {
-    siteSpec {
-        baseUrl = 'https://example.com'
-    }
-}
+build(name: 'production', extending: 'mySiteAll') { }
 
-build('preview') {
-    siteSpec {
-        baseUrl = 'https://example.com/preview'
+build(name: 'preview', extending: 'mySiteAll') {
+    siteSpec { base ->
+        baseUrl = base.baseUrl + '/preview' // https://mysite.com/preview
     }
 }
diff --git a/cli/src/test/groovy/com/jessebrault/ssg/CliBasedStaticSiteGeneratorTests.groovy b/cli/src/test/groovy/com/jessebrault/ssg/CliBasedStaticSiteGeneratorTests.groovy
new file mode 100644
index 0000000..1f6d4d1
--- /dev/null
+++ b/cli/src/test/groovy/com/jessebrault/ssg/CliBasedStaticSiteGeneratorTests.groovy
@@ -0,0 +1,44 @@
+package com.jessebrault.ssg
+
+import com.jessebrault.ssg.util.Diagnostic
+import com.jessebrault.ssg.util.ResourceUtil
+import org.junit.jupiter.api.Test
+
+import static org.junit.jupiter.api.Assertions.assertEquals
+import static org.junit.jupiter.api.Assertions.assertTrue
+
+final class CliBasedStaticSiteGeneratorTests {
+
+    @Test
+    void meatyInitAndBuild() {
+        def tempDir = File.createTempDir()
+        SsgInit.init(tempDir, true)
+
+        def ssg = new CliBasedStaticSiteGenerator(
+                tempDir,
+                new File('ssgBuilds.groovy'),
+                [new File('buildSrc')],
+                [:]
+        )
+        def diagnostics = [] as Collection<Diagnostic>
+        assertTrue(ssg.doBuild('production', diagnostics.&addAll))
+        assertTrue(diagnostics.empty)
+
+        def buildDir = new File(tempDir, 'production')
+        assertTrue(buildDir.exists())
+        assertTrue(buildDir.directory)
+
+        def textOutputFile = new File(buildDir, 'hello.html')
+        assertTrue(textOutputFile.exists())
+        assertTrue(textOutputFile.file)
+        def pageOutputFile = new File(buildDir, 'page.html')
+        assertTrue(pageOutputFile.exists())
+        assertTrue(pageOutputFile.file)
+
+        def expectedText = ResourceUtil.loadResourceAsString('hello.html')
+        def expectedPage = ResourceUtil.loadResourceAsString('page.html')
+        assertEquals(expectedText, textOutputFile.text)
+        assertEquals(expectedPage, pageOutputFile.text)
+    }
+
+}
diff --git a/cli/src/test/groovy/com/jessebrault/ssg/StaticSiteGeneratorCliIntegrationTests.groovy b/cli/src/test/groovy/com/jessebrault/ssg/StaticSiteGeneratorCliIntegrationTests.groovy
index 4aa0a1e..71fe827 100644
--- a/cli/src/test/groovy/com/jessebrault/ssg/StaticSiteGeneratorCliIntegrationTests.groovy
+++ b/cli/src/test/groovy/com/jessebrault/ssg/StaticSiteGeneratorCliIntegrationTests.groovy
@@ -1,44 +1,6 @@
 package com.jessebrault.ssg
 
-import com.jessebrault.ssg.util.ResourceUtil
-import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.Disabled
 
-import static org.junit.jupiter.api.Assertions.assertEquals
-import static org.junit.jupiter.api.Assertions.assertTrue
-
-final class StaticSiteGeneratorCliIntegrationTests {
-
-    @Test
-    void meatyInitAndBuild() {
-        def tempDir = File.createTempDir()
-        SsgInit.init(tempDir, true)
-
-        def ssgBuild = new SsgBuild().tap {
-            it.cli = new StaticSiteGeneratorCli().tap {
-                it.logLevel = new StaticSiteGeneratorCli.LogLevel().tap {
-                    it.trace = true
-                }
-            }
-            it.baseDir = tempDir
-            it.requestedBuilds = ['production']
-        }
-        assertEquals(0, ssgBuild.call())
-
-        def buildDir = new File(tempDir, 'build')
-        assertTrue(buildDir.exists())
-        assertTrue(buildDir.directory)
-
-        def textOutputFile = new File(buildDir, 'hello.html')
-        assertTrue(textOutputFile.exists())
-        assertTrue(textOutputFile.file)
-        def pageOutputFile = new File(buildDir, 'page.html')
-        assertTrue(pageOutputFile.exists())
-        assertTrue(pageOutputFile.file)
-
-        def expectedText = ResourceUtil.loadResourceAsString('hello.html')
-        def expectedPage = ResourceUtil.loadResourceAsString('page.html')
-        assertEquals(expectedText, textOutputFile.text)
-        assertEquals(expectedPage, pageOutputFile)
-    }
-
-}
+@Disabled
+final class StaticSiteGeneratorCliIntegrationTests {}
diff --git a/cli/src/test/resources/page.html b/cli/src/test/resources/page.html
index 168e538..c7cf8c4 100644
--- a/cli/src/test/resources/page.html
+++ b/cli/src/test/resources/page.html
@@ -5,4 +5,4 @@
     <body>
         <h1>Hello, World!</h1>
     </body>
-</html>
+</html>
\ No newline at end of file