I had planned on using some extra fence boards for the siding, but it just occurred to me that I've read here that cedar shavings are not a safe bedding material . . . what about cedar boards? They're newish and do smell a little cedar-y, but they'll only be on two walls, and they should stop smelling after a little while. The coop will have one brick wall and one open side so there should be lots of ventilation. If the chicks are exposed to a little cedar smell for a short time, will it do them harm?