Since our coop has pretty high nests (it was a prebuilt one) I want to make sure the roost is high enough, but not so high they're hitting their heads. The coop is pretty small (see it here) so there isn't a lot of flexibility here. How much head clearance do heavy layers need? Will they need a ramp to the roost and/or nest boxes? The walls are about 4' high if that helps to visualize how far off the floor they are.