Seems like I have been saying this so much recently, order the Chicken Coops for Dummies book and it will show you how to make one. It has a ton of good advice about all kinds of stuff. It is well worth the money. If you decide to order the book, order it through BYC to show your support for the web site.
this is my brand new coop. tin roof with 3 roosting bars and egg boxes outside the coop with a liftable lid that can get eggs out of without going in the coop. The actual coop is 35 to 40 sq feet the run is 75 to 85 sq feet. The most expensive part of the whole thing was lining the inside with plywood over the actual frame of wood. It look better but it made the cost go up about 100$. The tin was expensive too spent about 75$ on it since it covers half the run too for shade. Then the feeder and waterer and the first food costy about 50$. In all i paid about 250$ for it all. The chickens were all given to me. the coop is very sturdy and it is water resistent. It is also very easy clean and we attached eye hooks to it so u can drag it with your car to move it. The design will hold about 12 chickens in all. if you getting bantams maybe 14 or 15. hope this helps.
Take a look at my profile page. We put ours ontop of a garden cart and it is easily moved around. We have the pen seperate but it butts right up to it. Seems to work fine for our 4 girls and they seem happy in it!