I found this block on a website. Hope it is the same as the one you are talking about.
http://how-to-quilt.com/patterns/dec2008patterns.pdf
Looking at it, it looks like you could cut 4" squares.
8 (4" squares) background
8 (4" squares) green
4 (4" squares) red-then subcut these into quarter square triangles by cutting both diagonals.(If you want one color-use green for these also.) You could do it with 2 squares and only sew these on the background, but I think I would sew them just as if they were red-but use green.
Or you could use 3 1/2" squares.