The coop you are describing was designed by Dennis Noonan-Harrison. I built one last summer. Type his name in the search engine and you can find his plans. He is very helpful. He sells his plans for $35.00 and they are very well done. I do not consider myself a very handy person, and it took me two full weekends and a few days to finish. I also made some modifications like a clean out door as I didn't want to have to drop the entire inside panel to clean it out. I opeted not to do the window with flower box either. Just a personal choice. If you go to Youtube and type Playhouse Coop you can see his videio. After you purchase his plans, he sends you a link to his page on Photo Bucket and there you find several pictures of the coop in various stages of completion.
After looking at the pictures, I made a modified version of the playhouse coop without the plans. It's a pretty simple design really. Like SewingDiva says I put the door on the gable end and then modified the door to the box with a slide/spring mechanism so I can open/close it without going into the run. You can make it pretty cheaply if you have access to scrap wood too. Mine only ran ~$100 mostly for paint.