Check out johnbridge.com
Fiberglass 'receptors' are not (generally) intended to be tiled upon. They're mostly prefinished.
There are 2 ways to do a tiled floor:
1) mud bed + membrane
2) preformed shower base. Check out Kerdi from Schluter Systems. It's a 'foam' tray that gets cemented to the floor, protected with a membrane, and then tiled upon. It works in conjunction with a special drain also sold by Schluter.
You can find out all about it at jb or Schluter's website.
Shower floors needs to be properly sloped. You may be able to find a preformed base if your floor is one of the standard sizes. Custom or wonky shaped floors usually fare better with a mud floor.