Perches question

[the lemon tree]

How long of a perch (total) do I need per bird? I have a 4 X 4 coop for 4 chickens and am deciding how many/how long of a perch I should put in there. Also, what does the clearance need to be from the perch to the coop wall if I have a medium sized bird (in other words, how long/big is their butt). Lastly, the coop is only about 22 inch high with a ventilation window that takes up a few inches in height. What is the MINIMUM height I can set the perch so that their butt doesn't touch the ground when they are roosting? Again, these are minimum measurements since I do have a relatively sized coop and realize that the ideal height/length isn't really realistic in my case. Thank you!!

 

[flopshot]

with a 22" hight there's not much point in a roost but if you want to make them feel like there up higher make it around eight inches high and figure one foot per bird.