How wide is the fabric you want to use? I've done it using a 60 deg ruler, and also just using the 60 deg mark on a larger ruler. The ones I did - I think I used about 15" widths, so when I used a 60 deg ruler, I'd put a longer ruler on the side, move the angle one out of the way and make my cut.
When I do this pattern, I precut my fabric into the width I want - since usually I'm using a stripe fabric and need to cut it into lengthwise pieces first.