As a general rule you can't have too much roosting space. They recommend 1 foot per bird but you can't go too far wrong by doubling that.
My coops are at most about 4' tall from floor to rafters & since my birds like to roost as high as possible the main roosts are about a foot below the roof. I then put some bars a bit lower so they can leap-frog up more easily at dusk.
A lot of them like to sleep "outside" in the covered run, so I've accommodated them there as well. My permanent flock averages 32 birds & I probably have a total of at least 60' of roosting bars.
Inside the smaller of the coops at sunset, showing the top roosts & the rooster on one of the intermediate bars.
The early version of the roosting setup in the big coop, AKA "Fort Guinea." Since then I added two more bars (2x2) running the lenghtwise up top. The "ladder" setup below was a slide out which I've since replaced and I added three bars running crosswise across the whole coop for intermediate bars. Overall I try to have at least a 12" gap between the bars, ideally 16" to 18"
The "outside" roosts before I added the roof. It's sort of a jungle gym for them. Overall I like the 2x4's for long-term roosting, as they can completely cover their feet in the winter to ward off frostbite. The intermediate bars or "day roosts" I'll use 2x2's.
The top roosts are about 5' each. I've got 3 diagonals that are roughly 3' long in 3 of 4 corners. The birds seem to like using the diagonals to stage entry into the coop at dusk.
The bar the two legbars are preening on in the foreground is about 4' long & moveable (the base is made out of 4x4's), with some roughly 1' extensions all over it sort of like a jungle gym.
One thing I do with roosting bars is I try to watch how they use them, and often times I'll add more or change them up a bit if they have issues or they're fighting over a "choice spot."
For instance, last summer I had a guinea get completely lamed in one leg. While she was healing & hopping around on one foot I made a little "booster" bar out of part of the old ladder bar setup with a 2x4 tacked to part of it so she could get to one of the diagonals to roost at night until she got better.
The current "compound" as it sits now after adding the roof & the addition to the small coop. The interesting thing is that throughout the day the go back & forth between free ranging & here either to lay eggs or "cool off" if somebody is getting picked on.
I've also added roosting bars under my back deck, which I call "the bunker" because if they're feeling particularly threatened the bulk of the flock hides here. I think they like it because they can't be seen but can see out. The arrangement is also such they can fly from the roost to the front door of the run. You can see the edge of it in the upper left.
This arrangement is a grid with three 8' 2x2's lengthwise and four 4' 2x2's across. with six struts that attach to the deck joists.
