As you can see from the above posts, your dad has a choice to use Y-seams to make the blocks, or use a simpler method that puts a seam through some of the diamonds. I think the decision on which method to use depends partly on the fabrics selected (whether the seam would show up prominently and perhaps affect the design) and partly on how comfortable he feels making Y-seams. They're not really that hard, and he would get lots of practice making them on a tumbling blocks quilt.