Sailrite has some excellent videos to help you make your own cushions. On one of their videos I got a tip that has worked well in making patterns. First lay down some blue painters tape around the edge of the cushion area. Then lay some double sided tape like Sailrite's Seamstick on top of the blue tape. Then spread out their Duraskrim patterning material on top of the Seamstick. This allows you to reposition the pattern material and stretch it tight. At this point you are ready to use your magic marker to trace the edges and make notes on the pattern material every foot or so showing how much wider the top of the cushion will be due to the slope of the hull. When you are finished simply pull up the painters tape with no damage to the surface of the boat.