Here's my two cents, doubt its worth that much cuz I'm new at this, but...
Our 'Hen House Coop' is a converted shed with a belly button high 2 1/2' deep shelf on each side (aisle in the middle) that goes the entire 12 foot length. About 1/3 of each shelf has a lower shelf of the same depth as the top. This is a little bit lower than kneecap height. At this height are 2x4 braces.
(Okay before anyone thinks this was a thought out and planned structure, we happened to have a table made out of plywood that we just cut lengthwise down the middle and stuck in the shed.)
6 of the 14 hens like to roost on the knee high bars. ALL my Ameraucanas have opted for a shelf that is on the end of the shed and is about 2 feet from the roof. You should have seen my son and I searching for all the 'lost' Ameraucanas the evening they found that shelf! You cant imagine how QUIET they can be when they play Hide and Seek! or how loudly they cackled when we finally discovered them all watching us!
Anway, the most important part of my ramble is that our other pen, the one we have the smaller birds and a different rooster in has no shed. Instead we have some 'condos' that we built with doors and lids. For roosts in this pen, we took some old saw horses that werent good for anything else and mounted an old hand rail (wooden, like going up your steps) to it. For the smaller birds, we took another hand rail, mounted it on just a couple pieces of scrap wood and set it on the ground. They all just love the hand rails. Of course, my picture shows them sitting on the saw horse instead. LOL I now have quite a large stash of these handrails in the garage rafters for future perch projects.