How many fabrics do you plan to use in your log cabin blocks? (2?,4? A different one for each round? Each log different?) If using 1 1/2" strips you need 28 logs for your 7" block. (7 logs X 4 sides) if you are using a different fabric for each round ( one fabric for two sides, one for the other two sides, ...there are lots of ( variables) if you are using the same fabrics in all 144 blocks ( 12 across X 12down) then draw out a block, label it with your fabric choices and count how many logs you need of each fabric , I would figure 40" wide fabric strips, measure the logs on your drawn 7" block and add up the measurements for one fabric ( you can then see how many blocks you can get from each strip. You can cut 24 strips 1 1/2" wide from a yard of fabric. ( remember that 1/2" of your strip width is seam allowance so on your drawn block your logs should be 1" wide)