???? 8x8 or 64 sq ft at 4 sq ft per bird would be 16 birds. Maybe I misunderstood.
The 4 sq ft per bird in the coop and 10 in the run is really a minimum, and for adult birds. Our resident coop "expert" on BYC has about 10 sq ft per bird in the coop because she lives in Canada and they stay in all day part of the year, if my memory serves. Mine have more than the 4 sq ft and this is the south, their yard is well over 10 sq ft per bird, and I free range them as well, because they still picked the yard clean. Just for perspective, I have read that they need 87 sq ft per bird (no, not a typo, that much, really) if you want the grass and other plants to stay green and regenerate themselves.
I have more or less a 12x10 coop (sorry, don't remember, it's odd measurements) and 17 chickens, and have never wished for a separate storage area. Really, the chickens will appreciate the space. I store all my feed and supplies in the coop. A couple of metal garbage cans hold the feed, oyster shell, etc. A simple cabinet up high, too high for them to get on top of, would be nice, but I make do with the garbage cans. There is even a coop within a coop, a small area closed off with chicken wire for mamas and babies or whatever; it's maybe 3'x5'. (All was built with what was lying around so no measurements are exact.) The girls go in the coop in the heat of the day during the summer, unless they are in the woods. They also go in there during really hard rains, though will be out in the rain if it is a light one. I am really glad they have the space to be comfortable in there at will. No, they don't need that much room just to sleep or eat and drink.
I have also had about 50 in there, while they were young, til most of the roos went in the freezer. It was not too small at all for the young ones growing up.