I have pressure treated on anything that will touch the ground. The rest is regular construction lumber. We originally (or rather, DH originally..) built the coop as a playhouse for our children, and we didn't want them to be in contact a lot with the pressure treated lumber. Even if the coop was pressure treated, just use regular 2x4 for roosts, where they spend most of their time. If you have shavings on top of the flooring, they really won't even have contact w/the chemicals there.