Ibnzbass4 said:
Listen to these guys. There is a sticky link on the Replica Costumes Forum dealing entirely with Pepakura, and there is some really great information there. I am just trying it for the first time myself. You can get a Pepakura viewer free and even the Designer is free so long as you don't plan on saving any modifications you make regarding changing the scale of your build. And there are some free pep files created by vary talented members of this board for the comic and movie versions of Magneto's helm. Give it a shot. And pick up a pack of 110 lb paper/cardstock. It works great.
The resin is fiberglass resin you can get at Lowe's, Home Depot, etc, and it is a two-part compound that comes with hardener. Build your prop, coat it a few times with resin/hardener, fiberglass the interior and bondo the outside. Those are the basic steps.