I would definitely take advantage of the fact that you have two walls at an angle. Then you can get attachment points on two sides instead of one, which will be much more stable. Plus, you can make a slightly larger roof than otherwise; when you come home with heavy grocery bags in November and try to find your house key, you'll be grateful for it.
I would also make sure to get a bit of a slope on the roof, at least 6°. And preferably an extra gutter along that edge. It does break away from the rest of the architecture, but maybe it's worth it. It makes a big difference to avoid snow loads.
Material— I think that depends entirely on what fits aesthetically. One tip is to use corrugated sheet metal that looks like roof tiles; available at Byggmax, among others. If you use sheet metal or plastic, you will of course need to build a wooden frame, but you already know that.