Hi
SS4 is all about the namespace, so if you need to create ss template files for the classes that you create, you need to follow the trails.
For example, this is your subclass (of PageController)
<?php
namespace App\Web\Layout;
use PageController;
...
class MyPageController extends PageController {}
Then, the template you are looking for is
PROJECT_ROOT/themes/THEME_NAME/templates/App/Web/Layout/Layout/MyPageController.ss
or, you can override renderWith() function in your class to add more flexibilities (e.g. if x happens, I would like to use y.ss instead)
Hope this helps
Chees
Leo