I have a 32 by 24 pole barn I insulated. First I built false walls between the poles, 2X4 on 24". I insulated between the studs with rolled insulation then covered the walls with 7/16 OSB. For the ceiling I placed 2X6 between the trusses then put up white tin and filled the space with blown in insulation. For the door I glued foam insulation board against the tin.
The shop is easy to warm and keep warm in winter. As for nosy code inspectors, we do not have that here nor do we have permits. Which is a problem in its own right, I have seen some real horror stories in wiring.