I'm guessing that with a dog you're not too picky about the exact size, so you might start by just making nine patches that finish at 12 inches...then cut them down and do the disappearing act - the finished D9P block will be about 11.5 inches square if you do it this way. four blocks wide by five blocks long will make it about 44 X 55. You can easily find directions for cutting fabrics for the 12 inch finished 9-patch.