Here's an opinion from a non professional that's worth at least twice what you're paying for it! Instead of Tyvek, place some 1/2 inch foil covered insulation behind your metal panels. My builder (Morton) suggested this when I built my original 45 X 75 as I was going to build living quarters inside. He said it would deflect a lot of heat and would eliminate "sweating" of the roof panels. Not a lot of R value, but was a big help. I saw it used on side walls in a recent featured build on this site. I wouldn't think the Tyvek could do any harm, I just don't think it will help. My understanding is it's purpose is to fend off moisture while still allowing the walls to breathe. Not much breathing through steel panels. Chip.
