David says...

In a word, NO! Been there, done that. I had a shed that was hotter
than a firecracker when the sun came out. I painted the roof stark
white and put a thin layer of insulation on the inside of the roof. The
temperature drop was nearly unnoticeable. Years later I tore the shed
down and built my own. fiberglass shingle roof, 2 small gable vents,
thicker insulation AND I insulated the walls that were exposed to the
sun. Now on a HOT, HOT day I can walk into that shed and be greeted by
coolness akin to walking under a large shade tree.

If you don't insulate where the heat load is coming from you can forget
about cooling your shop. Of course the dark roof is much of the
problem, but the larger problem is lack of insulation.

Dave

I know renovation is probably the way to go, but I was hoping for a band
aid cure for now.