This pattern size can be increased by 12 stiches (the pattern repeat).
Hat requires 16 inch circular, Cowl 24 inch circular. Double Pointed Needles suggested to finish off hat in the end. The cowl can be made longer by increasing the 12 stitch pattern repeat to your cast on. Size will vary depending on the weight of yarn used. You can use cotton with wool. I used cotton for the white, and wool fingering for the red and grey because I wanted a spring hat for my niece.