Render menu in custom form-api module
I am not sure if I got you right,but if you want to call a form on a menu item.Here is view for that
Implement


  hook_menu() - to build custom page page callback - return your custom
  form here


Some sample code

function mymodulename_menu() {
  $items = array();
  $items['custom-menu'] = array(
    'title' =&gt; 'Your Custom Form',
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('mymodulename_custom_form'),
    'access callback' =&gt; TRUE,
    'access arguments' =&gt; array('access content'),
  );
  return $items;
}

function mymodulename_custom_form() {
  $form = array();
  // your custom form code goes here
  return $form;
}