Best way to do it, make a 3-D Pepakura pre-model. (for practice).
Do you have Pepakura Designer? if so, print out the 2-D images and fold the lines (use 110 lbs. cardstock). after you fold the lines, hot-glue or use rubber cement to put together your helmet base (the cardstock). resin up your cardstock helmet. after that, paper-mashay your helmet base. Use expanding foam (triple expanding foam) to fill your helmet to the size your head is (leave space for padding, fans etc., etc.) spray-paint and maybe...VWALA! you have a n00b
pepakura spartan 117 helmet. good for you.
P.S. i am not totally sure thats the way it goes, but give it a spin, and if i am wrong, someone kindly