Minimum recommendation is for 4 s.f. in coop per bird, and that's open floor space. While folks can and do run their space tighter, it sets them up for all sorts of behavioral problems. Do a thread search, and you'll see lots of threads from folks who are having issues with aggression that can be as sublime as the underdog not being allowed to come off the perch to eat, leading up to more overt aggression including feather picking, brutal bullying which can culminate in cannibalizing.