If you're going to build, why not build something that can be useful as more than a brooder? I built a 3 x 6 tractor that has been incredibly useful as both a brooder and a tractor, as well as a day time broody pen. I trained baby chicks to a cat carrier, and have used the cat carrier to shuttle them back and forth between big coop and the tractor when hawk predation made it impossible to get chicks outside any other way. BTW, it's super easy to train chicks to a cat carrier!
