I used smartsiding for my walls it's a composit version of osb with a t1-11 finish on the outside. it comes already primed and is gauranteed for 30yrs. homedepot and lowes both carry it for around $20 a sheet (4x8). looks nice, lasts and no splinters.
You can use cedar for walls if you like. The problem enlies in cedar shavings due to the strong smell (phenol compunds) they give off due to their large surface area. As long as your coop is ventilated, shouldn't be a problem as siding.
Thanks for the info folks. Construction is proceeding! DH has the 4 posts sunk (it's going to be a raised coop since the ground is not level and very rocky) and the floor built.
Chicks have been ordered (along with an extra 30 chicks for my sister who won't be able to pick them up for a couple weeks after I order them, Ack! What am I going to do with 45 chicks in my house!). Geeze, I hope I don't kill them. The "sick mcMurray chicks" thread is making me nervous.
You're suuure that was p/t? That's about what we pay up here for a sheet of 3/4" exterior-grade ply, and a quick google suggests the price is about the same in the States. Exterior-grade is not pressure-treated, it just uses waterproof glues to laminate the plies together (as opposed to regular, non exterior grade whose glue will disintegrate faster in the weather.)
There is supposedly such a thing as true pressure-treated plywood, where the wood plies are pressure-treated as well as the glue being waterproof, but I have to say that when I lived in upstate NY and now living in Ontario I never did manage to track down a source for such a thing (for other purposes). As PC says, heaven knows what it'd cost. There is marine-grade plywood but I am not sure whether that is pressure-treated, I *think* (someone correct me) it is just a higher grade of plywood with waterproof glue? Marine-grade is pretty expensive.
Anyhow, you should definitely use exterior-grade plywood for a coop (unless you can get the other kind for free and the coop doesn't have to last real long). But p/t plywood is certainly not necessary in any way shape or form, even if you can find and afford it.
Yes, pressure treated 3/4 inch CDX plywood was $36 for a 4x8 sheet. It's a low grade plywood but it is pressure treated with a preservative (copper, chromium, and arsenic in the form of salts) which is water borne and thus is applied to really wet lumber. This is why it is green and so heavy and damp when you buy it. Thus it should really be aired out for a few weeks before you put chicks in your coop.