Chickens like to be able to wrap their feet around a perch. So a perch about a inch or two in size is a good idea. I actually have 2x4 boards nailed across my coop for mine to roost on. I have a lower one, then a higher one, and they go from the low one on up to the highest. Hope this helps.
2"x2" boards are also good - just sand off the corners or use a router. It gives the chicken a little flat surface to stand on but is similar to a natural perch, better than a dowel. You can attach them to the wall using 2 1-foot 2"x4" boards to support. Good Luck!Susie
Simple, go out and cut some 1.5 inch green limbs. Natural to the chicken, and free