I would check out Pinterest for ideas. You just want to make sure that you have plenty of ventilation and it’s secure if you use something like an old play house. And obviously make sure there is plenty of room.
We have an old shed next to our house that at ONE point in the last 15 yrs or so, someone used it for chickens. I would not use it as it stands now. Too many holes and it’s basically falling apart. It used to be an old outside kitchen, so it has served its purpose. But to fix it for chickens now would mean basically buying a new building.
We recently started building a duck coop and used a shipping pallet. Not a regular sized one but this one held REALLY heavy objects. We have no idea what it held but it saved us a lot in material. I’m attaching a picture to show you what it looks like. The whole top part of the trailer is the pallet. We just took the thin plywood off and built a floor on it. Didn’t have to pay for the pallet, the company just wanted it gone.
We also go to auctions and get things we can use. But again you want to watch it and make sure what your getting is going to work. We just bought 30+ telephone poles cut down to 9’ long. We will be using these to lift the Brahma house up and for a fence for the yard.
