Below the directory structure we are using:

/
backend/
components/
        config/ environments/ main-private.php * main-prod.php    params-private.php *    params-prod.php      main-env.php *      main-local.php *     main.php      params-env.php *     params-local.php *     params.php     test.php         controllers/          SiteController.php ...
 
         ...
 
        extensions/
behaviors/
validators/
lib/
models/
FormModel.php