This is our coop, made for 3 chickens. The coop alone is 3x3 and the fenced in area is 6x3. We have 3 nesting boxes but that was a waste, they only use 1. It only cost us $20 for the hardware and chicken wire. We already had the lumber and metal. We have since added a PVC waterer and a feeder to the door. This is the first time we have ever owned chickens so we are still learning but a few of the most notable things I've learned from friends that have had large flocks for a long time are:
1) they love frozen fruits/veggies on hot days. We freeze melon after we cut the majority out and bananas without the peel. Be careful though because too much snacks like that can produce soft shells from lack of calcium. We learned that the hard way.
2) The place that they roost on needs to be wide and flat not round. Ours still don't use their roost so I'm not sure how necessary it is. They prefer to roost on the edge of their nesting box.
3) Make sure you can close up your coop if you live in a small town where critters live. We have a bob tail fox and made a small door to open/close every morning/night.
4) keep on the look out for mice. We switched to PvC feeders to a) keep the water clean (we bought the cup waterers instead of the nipple style) b) help eliminate waste. We had a huge mice problem (counted 7 in one night) and so doing PVC feeders has helped. If you can't do PVC feeders, try hanging them or make sure you leave it out of the coop at night.
We have had so much fun with it so far! Hope you enjoy it as well!!