I'm guessing he put the same shingles in the triangle that he intends to put on the roof, for continuity. If you don't like copper, you might consider slate, or a slate-like material. Good Luck!

May I suggest blocking out the triangle to create a recess that would then accommodate a 2x8 or 2x8 composite material (think deck boards) to trim out the alcove

I agree with ftlone, some sort of wood planking or accent material in just that space if it was flush with the trim would look nice

ftlone, I like your idea. Can you send me a picture, please, so that I can show to my buider. Thanks.

Sadly I do not have any photos which would illustrate it. In theory you would build a triangular, deep "picture frame" inside of the alcove using the 2x6, 2x8, or 2x10 depending on the depth of the recess. the 'glass' would be the plywood at the back. the part of the triangle parallel to the ground would tilted forward slightly to accommodate water run off.