Do you already have some chickens, or would this be your first flock?
I converted an old shed. For the brooder box, we used a cardboard box for the first couple of days. Panic set in when they suddenly sprouted little wings overnight. My husband grabbed some scrap wood and a roll of 1x2" welded wire he got for $5 (crazy deal) and built a large, wonderful home for them.
And when my rooster was injured, we used the brooder as a recovery pen for him, so it has served double duty for us. Now it's store on its side in the wood barn and is used as a storage box until the next time it's needed for the chickens.