Picture a piece of it bent sort of in this shape, just to get a basic idea of what I'm suggesting.
https://www.lowes.com/pd/Amerimax-Z-Bar-1-25-in-x-42-in-x-1-31-in-Aluminum-Z-Flashing/50019740If I was bending it I would not bend a 90 deg. angle where the stone and the wall meet, make it slightly less so the metal will sit at a slight slope for run off.
I'd snap a chalk line on the wall to mark where my metal will sit against the wall.
Where that area is that bends to cover up the outside edge I would do what's called a heam, simply means you bend the metal back over it's self to make it stronger and not wave when it gets hot.
Coil stock comes in many colors, in you case I'd be using black, it often comes black one one side, white on the other.
Once done the black will be less noticeable.
Any siding contractor could do this for you, or most HD's rents a brake, and you would just need to buy a pair of straight tin snips.
One last tip, measure along that whole wall before bending, there's likely to be one area that sticks out a little more, that's the measurement you want to use for all of your bends.
