code: private function createCreateForm(CustomField $entity, $type)
      {
          $form = $this->createForm('custom_field_choice', $entity, array(
              'action' => $this->generateUrl('customfield_create', 
                    array('type' => $type)),
              'method' => 'POST',
              'type' => $type,
              'group_widget' => ($entity->getCustomFieldsGroup()) ? 'hidden' :'entity'
          ));
          
          $form->add('submit', 'submit', array('label' => 'Create'));
  
          return $form;
      }
docs: Creates a form to create a CustomField entity.
  
  @param CustomField $entity The entity
  @param string
  @return \Symfony\Component\Form\Form The form