This pattern assumes you know enough to have already made the giant granny on your own. It also assumes you made the little shell things with three double-crochets (or what have you) and put 1 single crochet between each shell (two in the corners). I’m sure you can adjust this pattern to just about granny-square-making method you choose.

Guage is not important. Use the same hook and yarn you used for the rest of the granny square.