Here is my suggestion: Chuck up a 3/4" coving bit in your table. Adjust your bit height so the bottom of the cutting edge is at the centerline of your wood. Adjust your fence to reveal part of the bit and make a pass. Flip your wood and repeat. Keep adjusting the fence and flipping the wood until you have removed the depth needed. Odds are when you try fitting it to the roof you will need to do some hand chiseling for deformities in the metal anyways.