Here's one I built this summer. Coop floor is a 4 X 8 sheet of exterior grade subfloor. Back wall is 5 ft high, and front is 3 - used 2 sheets of T-11 for those walls. End walls were T&G boards that I had laying around. I built it with a run under to coop so they could have protection from the weather but still be outside if we don't let them out into the caged area. Once springtime is here, we'll put up nylon Electra-fence to let them "free-range" in fresh grass, and they'll still have the protection of the cage.
There's a sliding door in the floor and the ladies learned pretty quickly how to get in and out that way. In the spring need to make some adjustments to the sliding door - I planned on being able to open the end door and use a push rod to open and close it, but it loads up with poop and gets hard to open, so for now we're going into the cage to open and close it.
9 chickens and 3 nesting boxes. Generally, there're be 1 or 2 in a box at a time, so they load up 1 box with eggs, if someone can't wait, they'll use the other boxes.