Hello from Central Oregon!!
well the min per chicken inside a coop is 4 sq. ft. and and the run, if you have one, should be a 10 ft. min. per bird as well. Since the chicken math has started be prepared to make extra room for them so I would build a 8X10 and then have the nest boxes on the 10 ft side, one row long then have the poop board along that wall and then across the 8 ft side with the roost above that 6" off, with the poop board being two foot wide with the 2X4 roost centered, the on the 8 ft side of the coop you can put their food and water under the poop board so you have an open floor plan so that it can be cleaned easily, and I would use PDZ on the poop boards so you can sift the poop out to get rid of it. I hope that can help you a bit with a layout.