Follow the link in my signature below. We are all unique so there is no one size that suits all of us. Your climate, your other set-up such as run, how you manage them, your flock make-up, your goals, and many other things are all unique to you. The size that fits you may be totally different than the size that fits me. Coop size is not the important criteria, how much room they have when they need it that is important. That room could be the coop by itself, cop and run, or they could free range and sleep in trees.
I find the more room I give them the fewer behavioral problems I have to deal with, the more flexibility I have to deal with things that do come up, and I don’t have to work as hard. I’m all about taking the drama out of chickens keeping and making my life easier, but some people really enjoy the drama.