I'm a big fan of doing the coop first, and then you can brood in the coop.Which came first?
The brooder or the coop?
People who start with the brooder, and then get the chicks, tend to be building the coop in a hurry because the chicks are growing so fast. Then if anything slows down the building project, they have a bit of a problem because the chicks are outgrowing the brooder. Lots of things can go wrong unexpectedly (store needs to order material, rainstorm on the weekend scheduled to put up the roof, someone broke their toe by dropping the wrong thing on it, everyone catches the stomach flu, etc.)