depends on who you ask and what your general situation is. If they will be allowed to free range the majority of the time in the day then 2 square feet is good but if they are going to be confined to a coop or run then 4 square feet. There are many opinions on this and you will get a wide variety of anwsers. I have 15 and they will have a total daytime space of 72 square feet (coop and run combined 6'X12" restricted after dark to 6'X6' then morining run will open) Weather and bald eagle activity permitting they will be allowed in the yard as much as possible. The more space the better but I have friends that have more birds in less space than my coop and they don't have any issues with pecking. You should do 8'X8'X8' standard dimensions of lumber which equals less waste and more space.