Hipster
I'm Awesome
Looks like your going to need an L shaped piece of sheet metal. I have hand formed pieces like that by forming it over a piece of angle iron or piece of wood. Have also gone into an industrial fab shop and looked through their drop -off pile and had them put a a fold in a piece for small money. I work in a body shop so a lot of times I can find something with the shape I need in the scrap pile. A piece out of a hood, fender, rocker panel that has the shape you need. Just match up the thickness of the roof panel/piece you are replacing.