"hurricane ties" are required by code where I live. There are many different types. The ones I have used look like a bow tie where one end has been twisted 90 degrees. one end nails to the rafter and the other to the two wall top plates. They prevent the roof from flying off in high winds (hopefully). I have never had a problem making these work with birdmouths. Look a little harder in their catalogue and you will find ones that will work on your project. I think our code calls for one on at least every other rafter.