protected function getInstallationDirectory() {
    switch ($this->getProjectType()) {
      case 'drupal-module':
        return $this->getBuildDirectory() . '/modules/custom';

      case 'drupal-theme':
        return $this->getBuildDirectory() . '/themes/custom';

      case 'drupal-drush':
        return $this->getBuildDirectory() . '/sites/all/drush';

      default:
        throw new NotSupportedProjectTypeException();
    }
  }