I have made several in the past in various sizes from crib quilts to queen for a wedding gift. I did not add an extra 1/2" because the pattern I had at the time said that it was not needed to be added. That said, though, I have varied the sizes of each layer and the overall design to fit what I wanted. It's easy enough to design freehand if you'd like. I think you'll really like the method and your quilt when you are finished.