I am installing a 4' by 8' double shower in a master bathroom. I will be tiling all the walls as well as the floor. The floor right now is 3/4" cdx plywood with another layer of 1/2" cdx plywood over that for strength. I have a pvc pipe stubbed up in the middle for the floor drain, and that is as far as I know what to do. How do I build the floor so that it drains to the drain properly and not leak?