My design was roughly based on the Catawba Coops design, with some modifications to increase the interior space. It’s also a foot wider at the base. Beware of these design changes, however! You will wind up with a portable coop that isn’t really all that portable — I think ours weighs about 150 pounds. I also got inspiration from the many designs available on Backyard Chickens. Ours combines features from several different ones.
More details on my blog at Home Cheep Home.