Metal roof sandwich?

Hi I am currently in the middle of turning my old detached garage into a workshop. It has corrugated metal on roof and walls and is heavily rusted on roof but fine on the underside of the roof metal (plan on using rustoleum rusty metal primer for roof). I will be using spray foam to insulate the workshop. I really love the raw look of the metal and old pine boards on the inside and don’t want to cover the in side in spray foam. I have no plans to drywall the inside either. So I came up with a crazy idea of putting the spray foam on the outside of the metal roof then putting a new metal roof on top of that? Maybe same for the walls? Any ideas to save my aesthetically pleasing metal would be greatly appreciated. Nori