Am I wrong? Leave existing roof and do 'roof over'?

[GraceNC]

I have older mobile home in the process of renovating. Have 'contractor' who is making the home like a house- lots of concrete/brick/new floor joists, etc.

It's time for the roof- I have a dome..... contractor recommends an 'a' frame with a peak/ridge line, etc- not too much of a pitch but enough to make it look good and let the rain/snow go off.

The new roof will be metal; however, the roadblock is-

I've read countless places (even on here) that a new roof can be done while leaving the existing roof. My current roof has rust spots, holes here and there, etc- but ceiling trusses are good and solid.

He wants to remove the roof- saying things like leaving it will cause condensation problems.

Can anyone explain this to me? Will leaving the dome roof (just the thin metal from the '60s) cause issues? Should it be removed?

[Greg]

I would think that it COULD cause a condensation problem, but with proper insulation & ventilation the possibility should be a minimum. My concern would be a weight issue. How will the new roof be supported? Free standing (Pole barn type roof) or through the existing walls? If you are using the walls, make sure the wall studs & floor joists have enough support or better yet add extra.

Greg