I have 8 X 12 covered pens, some full size, some half size for bantams.
Some have coops, some don't but have plastic around to protect from cold and wind.
My bantam pens have 2, 4, and one has 5 chickens.
My standard pens have 4 BR's, 6(4 jg's, 2 red stars), and I have one with 5 japanese and 5 polish, so far no problems as they have been together since hatch but are next on the list to separate and put in a permanent fixture.
Anyway, all my chickens seem very content with their housing and I credit this to keepint the correct #'s so as not to overcrowd them.
Mine are in covered pens and even the ones with coops have open access from coop to run.
Space and #'s are the keys to having healthy chickens.
Individual breed and size are very important to determining how many and how much space, so it really depends on what you are planning on keeping.