Based on our own experience with rats, as well as those of our neighbors who had - and gave up - their chickens, I knew I had to design for rats, not for chickens. To me, that meant hardware cloth everywhere, or at least no gaps bigger than 1/2", and keeping the feed inside the coop, so there's no spilling food outside the coop. I also wanted an integrated coop and run so that there's never an open door to let the rats in, and I wanted it to be easy to clean when necessary. I wanted to have 4 or 5 birds with plenty of space, which meant the area needed to be about 50 sq. feet.
Those last few requirements meant it was going to have to be big, which was beginning to look cost-prohibitive until my neighbor decided to have his deck re-built. His carpenter had ripped up all the decking boards (5/4 x 6 treated wood) and tossed them in a roll-off bin. With my neighbor's permission, I helped myself and was able to cut down on the cost big time by repurposing the deck boards as siding.
Here are the plans, heavily influenced by the coops of other folks here on BYC:
The coop is 7' 6" square. I built it with a foundation of four concrete blocks as footings, on top of which is a 9' by 9' sheet of hardware cloth (three 3' by 9' runs, "stitched" together with wire), topped by a square foundation of ground-contact treated 4x4s. It sounds like overkill, but actually it's not that complicated. However, if I were to do it again, I think it would be simpler and not much more expensive to just pour a 4" slab foundation.
The 9x9 hardware cloth allowed me to wrap the hardware cloth up about 1 foot on all sides.
Then I framed the walls:
Assembled the walls on top of the 4x4s:
The completed coop:
I got real lucky with the door. I was planning to frame one myself to the somewhat randomly-sized opening in my front wall, but then discovered just how cheap a pre-fab screen door is at Home Depot. I was lucky in that the doorway I had framed was about 38" wide and 80-odd inches tall, and the pre-fab doors were 36" wide by about 78" tall, so a little furring in was all it took to make it fit perfectly. All I had to do then was fasten hardware cloth over the screen.
The front is completely open air, and the sides are open air above about 4 feet. If this chicken thing doesn't work out, I'll have the perfect setting for a living nativity in my backyard.
If you look closely at the roof in this picture and in the plans, you can see that I notched the purlins and rafters so that there are no gaps around the top - just in case the rats want to try climb the thing. The weakest point in the whole thing as far as rats are concerned is at the front and back of the roof, where the corrugated metal leaves 1" gaps above the outermost purlins. The only thing easily available to plug those is a foam product made to match the corrugations in the roofing metal. I'm a little concerned that the rats will eventually figure this weakness out and just chew through it. Until then, I'll be thinking of better sealants.
It complements our backyard nicely:
So far it is working out really well. Very low maintenance - the birds just get up in the morning and commence to feeding and whatever they want to do. No need to go let them out. I have a big enough feeder and waterer that we just do a daily check to make sure they haven't dumped over or drained their water, and refill water every 2 or 3 days. Super easy for asking the neighbor's kids to check on them while we are out of town.
I have added a run out in front where the hens can roam while we are working in the garden. It's just simple 2' high chicken wire with no top, so it requires a little supervision to watch for dogs and hawks. The hens get out there about once a week. I still need to add a nest box on the side.