Looking for roofing feedback —

I have a 100+ year old house in upstate NY with rough cut 2×4-2×6 rafters set 24″ on center topped with skip sheathing and metal shingles.  The shingles have been maintained over their life with fiber reinforced roofing paint — 1/4 thick at this stage.

The paint is failing miserably and I am trying to decide how best to address the problem.  I have received a quote to repaint but I was wondering if it is possible to tar paper over the existing paint and then add screw-on metal roofing?  The thought being that this would be the lightest addition that would give the longest lasting finish with the least amount of investment. 

Any help is appreciated.

jnelson, Ballston Spa, NY