So here we go:
You put two squares together right sides together and see a quarter inch seam the whole way around (even corners) and then cut along the diagonal. I used 10" squares, which made 6.5 inch squares. I needed three additional blocks so I cut 7" squares and then cut them on the diagonal and sewed two together on the diagonal. This have me my 21 purple/white blocks, 21 purple/green, and 21 green/white.
You can kind of see my chicken scratch layout and calculations. I'm a visual person. I have to see it before I can do it. I'm sure it makes zero sense to you but it's perfectly clear to me ;).
It is very important to square up your blocks! I used a 12.5" quilters square ruler. Even though I used my 1/4" foot, some of my blocks were almost 1/2" big and some were just barely the right size. Agh!
Next up: layout! .....