The program that's almost always used for paper/cardstock building is Pepakura Designer/Pepakura Viewer. The designer is used to "unfold" 3D models, which can then be printed onto heavyweight paper, cut out, and glued together. then comes a long process of resin, fiberglass, sanding, and repeating, usually with some Bondo thrown in for good measure (obviously nasty stuff for your lungs unless you use the right safety equipment... you don't want your actual voice to sound just like Grievous)
If you haven't seen examples, http://skipspepakuracostumes.blogspot.com/
sells quite likely the most impressive models I've ever seen (and according to the side of the page, Skip does commissions too!) One of the first things listed there at the time of this post is a snow clone helmet he modeled, unfolded, printed, and assembled.
The owner of/guy who does all the work for that site is a member here, so if you PM him (or he finds this topic), I believe he'll be willing to help in more detail.
One other thing: The place with the most info on this method is probably the 405th forums. They're based on Halo, but have a lot of general info on Pepakura armor.
Hopefully this helped teach you some things you didn't already know!