I have gone through a few coop designs, all of which were built from scratch from old materials. And now I am thinking of building a new coop.
The first coop was a square cubby house made of old wooden pallets and star pickets, built into the corner of my backyard against the side fence and tool shed. My pullets roosted on branches I laid across the gaps between the pallet planks. I nicknamed the coop the 'Nesting Nook'.
The second coop was repurposed from part of a daybed I had bought to use inside the house. I bolted parts of it into an arch and covered the outside with mesh and then shadecloth. The idea was for it to provide shade throughout the day. But soon I found them all roosting on top of it! They would even sleep on top of it during rain at night!
The third coop was that shade arch that I leaned against the side of the first coop, then bolted it down. The tool shed formed the back wall of this coop. I made a small ladder out of wooden branches so they could climb up. The chooks would roost on the edge of the Nesting Nook as a ledge. This ledge became a problem because they ended up roosting amongst their poop, which I considered to be unhygienic, and was a nightmare to clean.
The fourth coop, the current coop, is a corner of my tool shed. I closed off the corner with wooden pallets as walls, then square mesh up to the roof. One section has tree netting hanging down as a door, secured by hooking it over long screws. Inside the coop is a large tree branch that sits horizontally across the corner, about 1.5m off the ground. This is their perch. I built a big ladder out of branches and screws, that they climb up to get to the perch for roosting at night.
There is straw and dead leaves on the floor to catch the poop, which I muck out and replace when required.
I cut a hole in the side of the shed for their doorway - they enter the coop by first walking through the Nesting Nook (their first coop, on the opposite side of the shed wall, outside), then through the doorway.
I really like this coop, however I am thinking to build a separate small shed for them with nesting boxes and a big perch, for a new coop.