notch the rafters over the beams instead of notching the beams to accept the rafters. this is called the birdsmouth cut and can be laid out easily with a speed square. This will maintain the integrity of the beams. I'll assume judging by how good your drawing are you wont have any trouble calculating the rafter lengths or distance between the cuts but if you do, let me know. Stick framing roofs is both fun and challenging, but anyone with a good grasp of gemoetry can do it. Good luck.