I read somewhere, but can't find it, how many square feet you need per bird...or is it cubic feet? I can't remember. We plan to have 12 chickens, but planning for chicken math, my husband wants to build a coop for 16. What is the smallest amount of space we would need? (not saying we're going to make it that small, my husband just wants a starting point). How many nesting boxes would we need? Not all of our chickens will be layers, only a few will (maybe 4 or 5?). Thanks!!