I built a firewood rack out of pressure treated 2x4's. I made a corrugated metal roof for it with a wooden frame that became terribly warped after a few months. I took the roof apart to rebuild it but the 10' pieces of 2x4 I bought to use are starting to warp after sitting in my driveway for 2 weeks waiting for me to get around to rebuilding it.

Any tips on either selecting better lumber or drying them in a way that discourages warping?

My other thought was to use cedar for these two pieces. Would that be better since it seems like it's already drier when I select them at the lumber store?

I think a lot of ambient factors can affect how your pressure-treated lumber warps as it dries. We have a dry climate, and I've had decent luck keeping PT lumber flat and under some weight of other lumber. Personally, I've also had much better luck with PT lumber retaining shape when it was installed in a manner that kept it rigid in multiple directions (ie a bottom plate). It sounds like your roof configuration doesn't do this and I bet you'll struggle with it no matter how you "dry" it.

I think you're on the right track with cedar as it's relatively warp resistant and naturally rot resistant. I'd try fencing suppliers as they've got usually go better selection for dimensional cedar over big box stores.

Thanks, Ben. I may run up to Lowe's and just flagrantly some cedar boards. Shouldn't be too pricey. I've never used cedar so I'm glad to hear you confirm it's less prone to warp. That should solve my problem!

Make sure you buy treated lumber labeled KDAT, kiln dried after treatment. A bit more expensive but wet lumber will turn much worse as it dries.

Thanks, HillCountry. I have never heard of that. I'll have to look for that. I rebuilt my deck this past spring and have several pieces I need to replace due to excessive warping or shrinkage.

For this firewood rack roof I just went ahead and used cedar. I think it will be perfect. Thanks again.

Own a lumberyard.

The other advice is get 2 x 4's installed right away as the construction / bracing will help.

Agree and if not a top knotch lumber yard ala this or my granddad, then never Lowes, maybe Home Depot and pay for "ground contact", then cherry-pick em

Fun fact
http://rb.gy/m8n74
got any clamps?

A tool that just adds to the expense is a moisture meter. But it can help to make sure the lumber is properly dried.
Also check the grain structure. There are some YT videos about this. Some grain directions are more prone to cupping, bowing, or warping.
Also, depending what tools you might have, buying larger stock like 2x10s tend to be more stable (larger trees and heartwood) but you need to be able to rip them to size.