If the finished block size of 12” then a 7 X 8 layout will give you an 84 X 96. So you just need to make one more block. You can always finish it off with a border if you want it a bit bigger. For the layout, find a place you can lay the blocks and take a picture on your phone. Then look at the picture to see if you want to make any changes. You get a better view of it this way.