We bought a med/lrg wooden doghouse from the feed store (it*s a little bigger than 2x3 ft.) and raised it up on 2x4s about 20 inches. Hubby cut a 3x10 inch vent over the door and another on the opposite side which I covered in wire. He then cut a large access door that folds down on hinges on one of the long sides. The run is made from 2x2s and is removable (we secure it with 5 spring-closing hook-and-eye fasteners) and attaches from the top of the dog door/pop hole. Everything is covered by 1x1 welded wire--top, sides and bottom, including the underside of the coop. The total run and under coop area is about 2 1/2 ft by 7ft. It wasn*t hard to do, it just took a few days for us non-construction folks to put it together. We actualy did it in stages--Hubby made a wire door to cover the opening and the birds lived in there for a while before we modified the dog house and then built the run a few weeks later.
I like having complete side access to the inside of the coop and I really like having ample room under the coop for the waterer and feeder. The girls seem happy and they get a lot of free time out in the yard so the little set-up is working well for my Welsummer and two silkies. Good luck!