For me, it's far easier to just take a digital photo of the quilt, print it out as a full page (gray scale so I'm looking at values, not hues) and doodle on the quilt until I find something I like.
IF I have repeating blocks and want my quilting design to relate to the blocks, I will just put the block on my scanner (or a photocopy machine) and print out several copies. Again I play around and doodle on those with a marker until I find a design I like. The actual doodling helps create a brain/movement connection and makes the free motion quilting come more smoothly.
RST