Thinking of making my roost with 2x4's. That will give my girls a flat for their feet. Is there anything wrong with doing so? It will be 3 or 4 levels high. About 4' tall for the highest level and lowest being around a foot off the floor.
If you live in a cold winter climate, 2x4's are perfect, with the larger, flat side up so the birds can cover their feet when they sleep. If you make the roosts on different levels, you will have dominant birds up high, and lower level birds down lower. For this reason, and to cut down on fighting, some people put all of the roosts at the same level.
I rip the timber down the center of the 6 inch wide flat on my table saw, making a roost pole with a small curve on the top part that is 3X4 inches. The 4 inch part is still flat enough for a hen or pullet to cover her tootsies with her feathers during cold weather but you have better drainage of any blowing snow or sleet melting off the roost pole and this helps keep toes from freezing. And I think that it is more natural for the chicken.