There was another thread where we were talking briefly about building the "mandible" pieces to the arbiter/elite helmet. I can't seem to find it atm, but ill keep looking. Link is working on the legendary skull/shield, and he was just creating those pieces for his. I think he actually attached them right to the helmet. Aside from that though, if you wanted the mandibles to be a different texture, or feel, you could create them seperatly to give them more of an organic feel.
As far as scratch building. I would personally take some kind of paper or cardboard with a cylinder shape, and use a half of it to create a rough shape, then detail it and reinforce it with some fiberglass or so. Similar to how the MC vents are done.