You can get away with 2 sq ft per bird. However, you might end up with behavior problems such as pecking, fighting, stress, and feather pulling. Even 4 sq ft is what many consider the very minimum to have. For the run 10 sq ft per bird is suggested. You will need your roosts to be higher than your nesting boxes. Otherwise the chickens will try to sleep in the boxes instead of on the roosts. They like to sleep in the highest place they can get. Anyway, with chickens remember one thing. Bigger is always better because you are going to end up with more chickens than you thought. They call it chicken math.
For example, I have a 6 x 8 foot coop. At 48 sq ft it was built for 12 birds. My nesting boxes hang on the outside so that is all area for the birds. Well, Gary's sister asked me to take in a few of her chicks as she was out of room. They ended up being pullets so I am keeping them. So my 4 sq ft per bird is gone. I have 15 birds so it really isn't too bad. My run is 14 x 8 ft, 112 sq ft which was supposed to hold 12 birds (yes it was 8 sq ft short, I blame the builder, my neighbor). I do have a 3rd area for the birds. I surrounded an area of about 1,000 sq ft with that electric poultry netting. They have that area to roam in every day. Of course when it's snowing they prefer to stay in the covered run. It was near the end of the winter before they were brave enough to walk on snow.
I have 2 roosts, each 6 feet long made from 2 x 4's. Of course, chickens being chickens they only like and use one of those roosts. And of course, chickens being chickens they have decided that only half that roost is good. So they all try to crowd onto about 3 1/2 feet of one roost. That means they are sleeping on top of each other and don't seem to mind it a bit. It's like that with nesting boxes too. When I had 2 boxes they all used just one. Now that I have 3 boxes, they only use 2. Chickens have their own peculiar way of doing things.