I understand where you are coming from wanting more chickens than than you have space for. I get it - I was there, built a bigger coop and could easily be there again. I know some of the people of BYC that I respect the most say 4 feet is the number. The internet says you can do it in 2 feet...
Well you know when they get the new coop built then the other coop willl be empty and it wil have to have chickens too. So if you add the 4 x4 coop and the 4 x 8 coop dimensions together then you have 50 square feet.
They say 4 feet per chicken so that would be 12 which they already have...