What OGM said.
You might follow the link in my signature for some of my thoughts on space requirements. I don’t believe in the 4 square feet guideline, it’s just a starting place. How much room you need depends on all kinds of different things. We are all unique. We keep them so many different ways that no one number is right for all of us. Space doesn’t just mean coop, it means how much room they have available when they need it. That could be coop, coop plus run, or something else.
I’ve found that the more I crowd them the more behavior problems I have to deal with, the less flexibility I have to deal with them, and the harder I have to work taking care of them.
If you are buying new building materials, the most economical generally come in 4’ or 8’ dimensions. You can usually save a lot of cutting and waste if you design around those dimensions. Your foundations and roof have to be accounted for but you can generally build an 8’x8’ instead of a 7’x7’ for almost no extra money and probably less work since you are not cutting as much. A 12’ dimension isn’t too bad either.