I built one as well (with polycarbonate visor) out of a DP mask, but to be safe, tested it OFF of my head first. the first shot to the forehead area from 20 feet went right through the dome, splattering paint all on the inside! not recommended, unless built from scratch out of better materials.
I am going to try and work with a fiberglass Clone Scout Trooper (green camo) helmet as my next paintball helmet, using real JT goggles on the outside.