Should I tear down rafters framed with pressure-treated lumber and start over?

Leave them up. You bought yourself heavier and more expensive rafters than you needed, but tearing it all down and eating a restocking fee is just burning cash twice.

The only critical detail you have to address right now is the hardware. The chemicals in modern pressure-treated lumber will chew thru standard bright framing nails in no time. Pull whatever untreated nails you tacked up and switch over exclusively to hot-dipped galvanized or stainless steel fasteners. That goes for your framing nails, rafter ties, hurricane clips, and the nails you use for the sheathing.

As for the lumber twisting: wet treated stock only turns into pretzels when it sits unbound in a loose pile under the sun. You prevent that by locking the structure togather before it has time to shrink. Run a row of solid blocking mid-span to keep the centers dead plumb, nail your sub-fascia across the rafter tails, and get your roof decking sheeted as soon as possable. Once the plywood is nailed down every 6 inches on the edges and 12 in the field, those 2x6s physically cannot roll. They will dry out in place over the next few months right where you pinned them.

Inspectors won't fail you for it, either. #2 pressure-treated lumber carries the exact same structural load and span ratings as standard untreated Doug fir of the same grade. Don't overthink this. Fix your fasteners, get it locked down with sheathing, and keep rolling.

Totally agree with locking it down imediately, but keep your interior timeline in mind too. Don't rush to insulate or drywall the ceiling underneath. That wet treated stock is holding an absurd amount of water. If you sheath the top and seal the bottom with poly and sheetrock too quick, you'll trap all that moisture inside the rafter bays and invite mold. Deck it, dry it in from the weather, but let the underside breathe with plenty of airflow for a month or two before closing it up.

If those wet 2x6s are already fighting you and crowning while you set them, skip beating on framing nails to muscle them straight. Pick up a box of FastenMaster TimberLOK structural screws. The hex drive bites hard and will suck a stubborn, wet rafter dead flat against your plates without splitting out the grain. Plus thier proprietary coating is fully rated for ACQ pressure-treated lumber, so zero corrosion worries down the road.

Man I'm learning so much just reading thru this! Never even realized you coud leave PT rafters up like that without an inspector completly red-tagging the whole job. Quick question since you're cutting all those rafter tails and birdsmouths right now—does that super wet treated stuff gum up circular saw blades crazy fast? I'm gearing up to frame my very first lean-to shed next month and wondering if I need to stock up on special blades or if regular Diablo framing blades handle wet treated lumber without bogging the motor down?

Watch your depths when you tie into existing framing. Fresh wet PT 2x6s are easily swollen to 5-5/8" or even 5-3/4" deep right off the bunks. Once they cure down to around 12-15% MC, they’ll drop a solid 1/8" across the grain. If you plan on running a flat drywall ceiling directly to the bottoms later, keep an eye out for uneven planes before you rock it. Also, check your hanger stamps at the yard. Make sure you're buying Simpson ZMAX with the 'Z' suffix, like the LUC26Z or H2.5AZ. Standard G90 galvanization won't hold up long-term against the copper levels in modern treated stock.