HI, please don't post topics like this, there are some many stickies that can help you. Did you watch Adam's video.
You can mold it and cast it. Make a base out of clay and mold it, then cast it. But Pepakura is actually really good. I mean i first didn't like it either, but it's cheap and you can make it as accurate as The halo armor in H3.
Why do you want to make it accurate. That takes a lot of work, just add what you like, it gives you indivdiualalitty, than just oh it's master chief, still the same but it looks cool. Or woah nice paint job and details : Thumbs Up:
Use pepakura, you can even make it look like a cast