I would do it the same way luvspaper described. Each 36 patch block would be made from a 6 strip unit (3 strips of each of the two colors alternating). After sewing the six WOF strips together, cross-cut that 6-strip unit into 12 1/2" squares (you will get 3 per 6-strip unit). This is what I did for my triple irish chain quilt, and it worked great--sure beats trying to sew individual 2 1/2" squares together!!