Well, then, maybe you should back up and rethink. Your coop may be large enough for all of them; you may not need a separate building at all. If you have an opensided coop with run attached, they won't need any 4 sq ft per bird in the enclosed area, only enough room to roost out of the weather, and maybe to get the feed and nests out of the weather. That looks like a pretty good sized building from the photo. I imagine in your climate it would be unusual for them to stay indoors all day.
