that could be an easy 12" block.
4" square, bordered by 4" x 2" rectangles, with a 2" square corner stone.
make four of them for each block, rotating them to form the design you want.
don't forget to add your seam allowances, so cut:
4.5" squares
2.5" squares
4.5" x 2.5" rectangles
a similar block is the Hayes Corner:
http://www.quilterscache.com/H/HayesCornerBlock.html