Index: resources/sql/autopatches/20150715.harbor.1.buildparam.sql
===================================================================
--- /dev/null
+++ resources/sql/autopatches/20150715.harbor.1.buildparam.sql
@@ -0,0 +1,6 @@
+ALTER TABLE {$NAMESPACE}_harbormaster.harbormaster_build
+  ADD buildParameters LONGTEXT COLLATE {$COLLATE_TEXT} NOT NULL;
+
+ALTER TABLE {$NAMESPACE}_harbormaster.harbormaster_build
+  ADD buildParametersHash VARCHAR(32) COLLATE {$COLLATE_TEXT}
+  NOT NULL DEFAULT '2c08d653e1ee60d55cd0da551026ea56';
Index: src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
===================================================================
--- src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
+++ src/applications/harbormaster/controller/HarbormasterBuildableViewController.php
@@ -191,6 +191,10 @@
         HarbormasterBuild::getBuildStatusName($status));
 
       $item->addAttribute(HarbormasterBuild::getBuildStatusName($status));
+      $parameters = $build->getBuildParametersAsString();
+      if ($parameters !== '') {
+        $item->addAttribute($parameters);
+      }
 
       if ($build->isRestarting()) {
         $item->addIcon('fa-repeat', pht('Restarting'));
Index: src/applications/harbormaster/step/HarbormasterRunBuildPlanBuildImplementation.php
===================================================================
--- src/applications/harbormaster/step/HarbormasterRunBuildPlanBuildImplementation.php
+++ src/applications/harbormaster/step/HarbormasterRunBuildPlanBuildImplementation.php
@@ -33,12 +33,39 @@
       $name);
   }
 
+  public static function parseParameters($text) {
+    if (trim($text) === '') {
+      return array();
+    }
+
+    $pairs = phutil_split_lines($text);
+    $attributes = array();
+
+    foreach ($pairs as $line) {
+      $kv = explode('=', $line, 2);
+      if (count($kv) === 0) {
+        continue;
+      } else if (count($kv) === 1) {
+        $attributes[$kv[0]] = true;
+      } else {
+        $attributes[$kv[0]] = trim($kv[1]);
+      }
+    }
+
+    return $attributes;
+  }
+
   public function execute(
     HarbormasterBuild $build,
     HarbormasterBuildTarget $build_target) {
 
     $target_plan_id = $this->getSetting('id');
 
+    $parameters = self::parseParameters(
+      $this->getSetting('parameters'));
+    $parameters_hash =
+      HarbormasterBuild::getBuildParametersHashForArray($parameters);
+
     // Get the target build plan type.
     $target_plan = id(new HarbormasterBuildPlanQuery())
       ->setViewer(PhabricatorUser::getOmnipotentUser())
@@ -64,7 +91,8 @@
     // Find the build for that build plan (if it exists).
     $target_build = null;
     foreach ($other_builds as $other_build) {
-      if ($other_build->getBuildPlanPHID() === $target_plan->getPHID()) {
+      if ($other_build->getBuildPlanPHID() === $target_plan->getPHID() &&
+        $other_build->getBuildParametersHash() === $parameters_hash) {
         $target_build = $other_build;
         break;
       }
@@ -73,7 +101,9 @@
     if ($target_build === null) {
       // There is no current build with this build plan on the buildable,
       // so now we're going to start one.
-      $target_build = $build->getBuildable()->applyPlan($target_plan);
+      $target_build = $build->getBuildable()->applyPlan(
+        $target_plan,
+        $parameters);
     } else {
       // If the build plan has failed on a previous run, restart it.
       switch ($target_build->getBuildStatus()) {
@@ -162,6 +192,14 @@
         'type' => 'text',
         'required' => true,
       ),
+      'parameters' => array(
+        'name' => pht('Build Plan Parameters'),
+        'type' => 'textarea',
+        'caption' => pht(
+          'A newline separated list of parameters to pass into the build.  '.
+          'Each attribute should be specified in a key=value format.'),
+        'monospace' => true,
+      ),
     );
   }
 
Index: src/applications/harbormaster/storage/HarbormasterBuildable.php
===================================================================
--- src/applications/harbormaster/storage/HarbormasterBuildable.php
+++ src/applications/harbormaster/storage/HarbormasterBuildable.php
@@ -136,11 +136,19 @@
     }
   }
 
-  public function applyPlan(HarbormasterBuildPlan $plan) {
+  public function applyPlan(
+    HarbormasterBuildPlan $plan,
+    array $parameters = null) {
+
+    if ($parameters === null) {
+      $parameters = array();
+    }
+
     $viewer = PhabricatorUser::getOmnipotentUser();
     $build = HarbormasterBuild::initializeNewBuild($viewer)
       ->setBuildablePHID($this->getPHID())
       ->setBuildPlanPHID($plan->getPHID())
+      ->setBuildParameters($parameters)
       ->setBuildStatus(HarbormasterBuild::STATUS_PENDING);
 
     $auto_key = $plan->getPlanAutoKey();
Index: src/applications/harbormaster/storage/build/HarbormasterBuild.php
===================================================================
--- src/applications/harbormaster/storage/build/HarbormasterBuild.php
+++ src/applications/harbormaster/storage/build/HarbormasterBuild.php
@@ -9,6 +9,8 @@
   protected $buildPlanPHID;
   protected $buildStatus;
   protected $buildGeneration;
+  protected $buildParameters;
+  protected $buildParametersHash;
   protected $planAutoKey;
 
   private $buildable = self::ATTACHABLE;
@@ -138,10 +140,35 @@
     }
   }
 
-  public static function initializeNewBuild(PhabricatorUser $actor) {
+  public static function initializeNewBuild(
+    PhabricatorUser $actor) {
     return id(new HarbormasterBuild())
       ->setBuildStatus(self::STATUS_INACTIVE)
-      ->setBuildGeneration(0);
+      ->setBuildGeneration(0)
+      ->setBuildParameters(array());
+  }
+
+  public function setBuildParameters(array $parameters) {
+    $this->buildParameters = $parameters;
+    $this->buildParametersHash =
+      self::getBuildParametersHashForArray($parameters);
+    return $this;
+  }
+
+  public function getBuildParametersAsString() {
+    $strs = array();
+    $parameters = $this->buildParameters;
+    if ($parameters === null) {
+      $parameters = array();
+    }
+    foreach ($parameters as $key => $value) {
+      $strs[] = $key.'='.$value;
+    }
+    return implode(', ', $strs);
+  }
+
+  public static function getBuildParametersHashForArray(array $parameters) {
+    return md5(print_r($parameters, true));
   }
 
   public function delete() {
@@ -156,9 +183,14 @@
   protected function getConfiguration() {
     return array(
       self::CONFIG_AUX_PHID => true,
+      self::CONFIG_SERIALIZATION => array(
+        'buildParameters' => self::SERIALIZATION_JSON,
+      ),
       self::CONFIG_COLUMN_SCHEMA => array(
         'buildStatus' => 'text32',
         'buildGeneration' => 'uint32',
+        'buildParameters' => 'text',
+        'buildParametersHash' => 'text32',
         'planAutoKey' => 'text32?',
       ),
       self::CONFIG_KEY_SCHEMA => array(
@@ -272,6 +304,11 @@
   }
 
   public function retrieveVariablesFromBuild() {
+    $parameters = $this->getBuildParameters();
+    if ($parameters === null) {
+      $parameters = array();
+    }
+
     $results = array(
       'buildable.diff' => null,
       'buildable.revision' => null,
@@ -281,7 +318,7 @@
       'repository.uri' => null,
       'step.timestamp' => null,
       'build.id' => null,
-    );
+    ) + $parameters;
 
     $buildable = $this->getBuildable();
     $object = $buildable->getBuildableObject();