I think the basic problem you have is that when you turn a block on point it is very much larger that the straight up block. So your 12" block on point becomes about 17". so to alternate 12" blocks straight and then on-point this would be 12" then 17" then 12" etc. Are you planning to square up on-point blocks? Rule is for setting squares- corner block size +2" and then cut diaginal. .For sides- Diaginal measurement of block +2" - cut 4. As Katier825 said. layout blocks and go from there.