How much more would metal roofing (good quzlity) cost applyed to bare roof
than fiber glass shingles?

There is a good discussion of this in the current (August) Consumer Reports.
For a DIY project there will be many caveats so do your research to be sure of
the results. Quality of the sheet with respect to gauge, coating materials will
be a prime factor. Treatment of cut edges, cutting tools are all
considerations. Besides standing seam there are architectural stampings in
steel and aluminum. The field right now is fascinating, so have fun looking it
over and post your results for the project. Good luck.

Joe