As far as I know it's not about coop design rather the run design. The idea is to keep chickens with fresh grasses and insects to forage while still keeping them contained, not free ranging. You create 3 to 4 areas with the first area being where feed, water, coop and dust baths are located. Off this main section you'd have 2 to 3 areas of penned in lawn. Let's denote the coop area as A with closeable access to forage areas B,C and D. You'd open the access from A to B for a few days then close it before it's over foraged to open access to forage area C for a few days then open access to only area D for forage for few days. This rotates the forage areas allowing time for the first area, B, to recover growth of grasses and replenish insects.
Basically your allowing managed free forage within runs. If chickens are given one huge area as a run they will eventually deplete everything worth foraging or more likely turn the area into a barren dust bowl.
I guess you could not have an area A and cut more doors in the coop to let them into different run areas each day to rotate. With this you'd need a big coop and likely leave water and feed in your coop so not to have to move them to different runs every day or two.