If they are four months old, why can't they just go in the coop?I've been using a big dog cage as a brooder for my chicks and just moved the whole thing into the coop with the older birds and I originally had the bottom of the dog cage in there but the chicks are very messy and I'm tired of cleaning it up. Is this fine for them? It will only be for a couple more months.
I'd also be worried about bumblefoot if using wire, but apparently some do, and it doesn't cause issues.