besides what PaperPrincess said, you probably would want to first sketch the design out so that you know the widths to add on either side to get the wave effect. I did basically the same thing you are attempting on a bargello--actually foudn that it's easier if you add the addition width into the block cuts (so instead of a 2.5" cut it would be 3", etc) but not sure how that impacts the use of the jelly rolls.