I would start with a starter coop. Do A LOT of lookin at diff designs. I built one last Oct thought it was the best. Then my cousin built a n a new one and I liked some of his ideas! A friend of minew just bought a new house and there was a 7X8 shed with it that he just gave me. I had to insulate run electricity make nest boxes and the thing I LOVE is on my first coop my chicken door is hinged from the outside which is also insulated. But on my new one I cut a hole for the door then it has a door that slides via a rope that I can operate from the door way instead of going in the fence area. But if I were to build from scratch it would be 8X8