Dutch Barn solution

Taking a new tack, could I ask what a good solution would be for the replacement of the rotting bargeboard and verge board on my shingle roof please (not the fascia - this is ok).
The building is a "Dutch Barn" style shack that SWMBO uses as a summerhouse (see pic).
I'd like to use PVC or some such material but I can't figure out how the roof will work. I guess the verge board keeps the shingle from blowing off even though they are stuck down.
Cheers.

Look for continuous dry verge

Thank you.
Will this work on this shingle roof where the shingles do not overlap the bargeboard?

You could put a bit of barge board flat on top of the shingles with the lip hanging over the verge.