Go buy lots of elmers glue, about 2 multi purpose white glue things will do the whole suit of armor, their 99 cents each at the store.
Resin the inside of the helmet lightly, then glue fiberglass to it, make sure you get lots of glue on each peice, do a thin line about every inch or so on your peice, then do it again sideways so it makes a squareish pattern of glue on your glass peice, then lay it inside, make sure it touches every nook and cranny for it to make the helmet strong, then once it's dried, glob resin on it until you cant see the glass, the glass should become the same color as the resin, then you can paint the outside...