I'd cut a rafter on the angle, top and bottom and lay it in place. Take a couple of scraps off the 2x 12 plate and lay them against the side of the rafter to see how they need to fit in place before notching the rafter. Also lay a scrap of sheathing on top of the rafter to see how it will fit into the scheme of things. Top and bottom, of course. Do this before you start cutting up a lot of wood!