Quote:
If you're going to leave the chicken door open at night and accept the risk that predators might break into your run and enter the coop through this door (and kill all your chickens), I don't think it makes any difference whether the chicken door is in the floor or in the wall. A hungry predator is going to find the door in the floor just as easily as it will find the door in the side of the coop.
As others have noted, one problem with a chicken door in the floor is the shavings falling out. Another problem noted is that you need to cut it a bit larger than if you were mounting the door in the wall because of the angle the chicken needs to use to get in and out using the ramp. You have to build a ramp, which is something you don't usually have to do with a side mounted door. And it's a bit trickier to build a way to close and lock a door in the floor, too. The final drawback I can see is that it uses up floor space, something that's quite valuable in a small coop where every square foot counts.
Sometimes you have no choice, as in when the run is completely under the coop. Personally, though, if I had the option I'd go for the side mounted door.