you can pretty much cut the squares any size you want. I've seen them any where from 4" to about 10" (so 4 2 inch blocks or 4 5 inch blocks + seam allowances) You can let the size of the repeat be your guide.
Often the blocks are fussy cut to get the showiest squares, so you are going to have some wasted fabric. I would take a couple of mirrors, tape them to make a hinge and audition the fabric with the mirrors.
Hmmm, not much concrete advice ;-)