Have you considered using the 'Square-in-a-Square' technique by Jodie Barrows? She sells a specialized ruler that is fantastic and usable for diamonds, squares and rectangles. It is an easy method to use and extremely versitle. A little pricey, but I think its worth every penny. I have made several quilts with this method and they came out great. I know I sound like an advertisement, but I really like the method. Makes wonderful pieces borders also. The best part - Bias edges are easy to deal with.