See here, his nose is at least a tail's length from the higher-up chicken's pooper. I really did measure my biggest chicken from nose to tail tip while she was roosting, and spaced those two roosts according to that measurement, so I'd have comfortable space for her to roost up high (where she likes it) comfortably with ample head room/turning room, also so her backseat driver won't have any risk of poop-de-doo in the middle of the night. I can't help it, I'm a nurse and poop is kind of my whole business. I don't want poop in any of the wrong places (like, in the eye).
Also in there is the top of the nestbox, all flat like a nest/shelf. some of the chickens like to cuddle there when its cold, they like the square with fresh pine chips to snuggle on.
I hope to build a run outside with a 6X6" post for a roost, set into concrete like a fencepost, with a good 2ft. roosting pole on each side of the post, starting 18" off the ground on one side, then the next roost 12" above that on the next side, etc spiraling up the 4 sides of the post so nobody can get pooped on while roosting, and all the poops right there around the post so easy for me to scoop up for my compost. Some chickens like to be up high, and some like to be down low. They each need their own favorite space.
I hope you can show pictures of what you wind up with!