IMHO chickens like a place to run under, from the sun or hawks or intrusive people. I build my coops with about 14-16 inches of clearance to the floor. I use the plastic lattice to close 3 sides. A piece of pvc goes through the holes to shoo birds when needed, and sweep them out. My tall coop is about 6 foot tall inside, with a step up to get inside, so there is no stooping. It has barnsiding for a roof, and stays well dry even with deep bedding. The inside floor is covered with a vinyl flooring scrap, (free form the trash) so water and poo are not soaking into the wood. With an inch or more of pine shavings, the birds skitter and scratch around, and basically mix up the poo and litter very well. A rake from the door way at low knee high, is quick cleaning into a small tarp, and funneled right into a 30 gal trash can. This mix is then spread on various parts of the garden.
So, the floor framing is extended by 2x4 posts in the corners, with angle bracing to a runner board of treated deck 5/4 x 6. My floor is 4x6, the runner board is rounded at the ends, to form skis, so the whole structure can be moved to a new area, and the fencing moved to encompass new grass.
Nest boxes are built in at floor level on one side (6) and about a foot above on the other side, added later as we got more birds. There is no roost in mine, but planning on a small 'A' roost in the middle.
