I agree that you should build BIGGER than you think you'll need--if possible. But, if you goof, who cares? Just add on, redo, etc. Just read the recent post regarding enough room for the birds in a "store-bought" coop, and I had to respond. I'm on this forum because I don't know enough experts to help me that live nearby. I DO know, however, that these birds are domestic. I have not handled my new (2 month olds) brood like I handle my dogs or horses. YET...they KNOW "Momkins" as the food-giver, even when my dog, Rose, harrasses them from the outside of the pen. Can't really release any of my horses, dogs, cats or chickens to the wild and tell them that they are "free" ('to pursue a life of religious fulfillment', or, whatever the excuse is today!) THEY'LL STARVE!!! (Well, maybe not Rose--she'll eat wild rabbit.) Not to anthropomorphize, but our animals have an "agreement" with us as to our expectations of each other. We feed them and they all have certain jobs. My cat, Tomkins, chose us to take him in when he was almost a week away from starvation at 5 months old. In exchange for nursing him back to health he mouses and he gets along with the others. We are the "government" and the animals are the "subjects." It's a benevolent dictatership. My hen lays eggs, like the young sister hens I'm now raising will also do. In exchange, I make sure that she(they) are fed, watered, and comfortably housed. Just food for thought.