I built this back in June for a robot themed party I had. The visor lights up, and the jaw moves with mine.
The helmet itself is constructed almost entirely from cardboard. I started with the two sides, roughly estimating the proper shape and size. They were connected by a separate strip of cardboard, sliced halfway in four places so it would bend in a jagged curve. Then I added another length of cardboard down the middle of the head, with semi-slices across every inch, so that in bent along the curve of my head.
I realize the detail I'm going in is already a bit too much, so I'll try and skim the rest since I don't have many pictures from when it was in pieces. There are smaller pieces from cereal boxes I used to cover up everything. The nose/cheeks area, is all actually one piece. The jaw is separate of course.
The eyepiece is a glow stick, which can be easily slid out. The great part is that this allows for me to easily change the colour to whatever I want. It's also relatively inexpensive.
To make the jaw move, I attached it with a flat pin. Elastics were attached to the inside, going from the cheek bones to the lower jaw. My jaw simply pushes down on the "jaw-piece" and the elastics pull it back up.
Sometimes I think it looked cooler when it was unpainted cardboard.