I don't know what's up with this forum but it hasn't notified me on this thread in a long time. I thought it died out a while back and had no idea people were still posting in it.
It's real easy for people to just say spray foam it but it's not easy to cough up $15k for spray foam. I even attempted to see what the ceiling alone would cost and that was $7-8k depending on who I talked to. These videos on youtube where the guys got these massive 2000sq/ft shops spray foamed for $4k are full of **** unless they knew someone or got it done pre covid.
I'm doing 2" polyiso foam board with the reflective side spaced 3/4" off the siding. I found a guy who sells factory rejects for a reasonable price. I'm using great stuff spray foam with the applicator gun to seal up the seams and then using foil tape to cover. I'm only about 1/3 done at the moment.
Covering the walls is a pain because the studs aren't 16 on center. They're anywhere from 4.5-5.5ft apart and it's random. I wound up finding a guy on marketplace selling corrugated metal sheets for 1/3 what Home Depot charges. I'm going to cover the walls up to 8ft with that and then use CDX sheathing to cover above that. I'd rather do drywall but I'm not going to waste 1/3 of each drywall sheet because of the stud spacing issue.