The block inspiration comes from Little Miss Shabby and her Scrapbuster Block. You can find her tutorial here. Feel free to insert your own 1 1/2" squares if you would like, as long as it goes with the colors.
As I carefully created this block, minding my 1/4" seams, my block squared up to be about 11 1/2" square. So that's what I'm hoping for with your block. If it doesn't come out 11 1/2", don't worry. Just send it in ~ I'm looking forward to your blocks!