new metal roof over old standing seam

I have recently talked to 2 different roofing companies about getting a new standing seam metal roof installed on my 1880s home. I currently have a standing seam roof and the seams appear to be about 16 apart. First roofer said that the easiest thing to do was instead of a tear-off, they would cut sheets of plywood to fit between the existing seams, and attach them on top of the old roof to create a flat surface, then top that with the new metal roof. They said this was a standard way of installing a second metal roof, and would give an added air space between the old roof and new. (but what about all the holes they would punch in the old roof?) Second company said they would do a complete tear-off of old roof, and install the new one directly onto the wood (replacing any as needed). Which is the correct way to install a new metal roof? Thanks!