Use Fiberglas insulation and a good vapor barrier. The vapor barrier and insulation will prevent condensation on the metal. The metal roof should have had the ribs vertical, not horizontal, and should have a moisture barrier under it. Spray foam would assure a dry ceiling with it the way it is. Spray foam is pricey, but the building is small, maybe foam it all.

I am looking into converting this metal building into a guest house. I was wondering how I would insulate the metal walls to prevent moisture from being trapped between the metal and the drywall. Thank you!