is it a kit? that stipulates to cut the log cabin strips across the pattern?
it does not matter which way you cut the fabric- perhaps you could fold it the lengthwise way & lay it with the blocks to see how you like it that way? can you post a picture so we could see the pattern? is it a small/narrow pattern? will you see it distinctly if you cut it with the pattern? does it change the look totally depending on which way it goes? it's hard to really say without actually seeing it...could be a personal choice- but i would at least try to (test) it both ways to get an idea how it will look