I'm planning to build a shower stall, and would like to know how much height I should have available under the floor for the trap and drain line. I'll be using 1 1/2" ABS pipe.

I'm planning to build a shower stall, and would like to know how much height I should have available under the floor for the trap and drain line. I'll be using 1 1/2" ABS pipe.

It's basically a 1/4 of an inch of fall per foot to the drain line -- And it needs to be a 2" trap and drain, not 1-1/2".