Good point Blue. Figure 10 sq foot per adult bird if they're normal sized. Bantams can get by with less. If y're planing to free range you can crowd them in a bit more since really they're only sleeping and nesting in the coop, but if you go by the 10 sq foot rule you should be good.Those prefab coop's don't hold up to higher wind's as they are not very well made for the most part. Also if they say it's good for 10 chicken's, most likely they are meaning 10 bantam's.