Depends really.
Are you going to have them in a permanent place, or do you want to move the coop/run around?
Are they going to be free range for a while in the day?
How big do you want the coop and run to be?
When we were building the coop (wooden), we were told that it needs to be big enough to hold 2 more hens than you are actually going to have so they have plenty of space to roost.
Ours is big enough for 16 so the maximum we could have is 14 - we had 12 at most at one point, now we have 11.
Oh and despite there being 3 perches to roost on, the girls
have to snuggle together on the highest perch!!