I am finnishing the coop and want to place the poop door through the floor. Wondering what size opening to use? The ramp will run down about 3' to the ground.
It'd be a lot better to put the popdoor thru the wall. You lose too much valuable floorspace with it there, also there is no way to prevent large quantities of bedding from falling out.
If for some reason you *have* to have it in the floor -- although that can nearly always be worked around -- make sure that there is something like 12++" clearance between the ramp and the floor, at the far side of the ramp. What hole size this implies depends on what ramp angle you have.