No vapor barrier

I'm in the process of purchasing a cabin in the mountains in Western North Carolina. The cabin was built in 1872 and then moved to this new location in the 70's. From the inside I can see what appears to be 1x12 boards covering the roof beams. From the outside you can see a corrugated metal roofing material. Rather than drop the price of the cabin the seller elected to put a new metal roof on. I asked what vapor barrier was used and was told the roofer said it was not necessary. My concern is that this new metal roofing material is being put down directly onto the 1x12 boards and that condensation will occur and rot the boards under the metal roof. I plan to somehow insulate the inside ceiling. Its not an attic but an cathedral ceiling so all heat will rise straight to whatever insulation I put in. Since I am not being given the option of paying for the roof I want my questions are. Will the new roof just condensate and ruin the 1x12's under the metal. Should I bite the bullet and just take the roof back off and put a vapor barrier with an air gap between the metal and the 1x12's. Can I use spray insulation on the inside or prevent any of the condensation from happening above it or will it just condensate between the insolation and the 1x12's. Just looking for words of wisdom from you experts.