Whatever you go with, make sure it's wide enough for the chickens to totally cover their feet when they roost (for winter time). Remember, chickens don't roost like many birds with toes curled around, gripping. They rest on the roost. A 2 x 4 laid flat, or even a 2 x 3 laid flat is wide enough for the feet, but not so wide that birds can poop on the roost, which is ideal. A 2x2 would be good for younger birds, or bantam breeds, but I personally wouldn't want them for full grown LF chickens. If you use branches, I'd go for 3 in. diameters or slightly larger...
