Quoting Ross Hemminger
HOW DID YOU MAKE THE HELMET!?!?
With some bricks, some white label stickers and some felt tip pens ;)
I based it round a cube, using the cube dude Rex for inspiration. The viser is made of black bricks and his antennae is some technic bricks with a claw arm holding it in. All the blue, grey and yellow markings are white sticky labels that I coloured using felt tip pens. Try it yourself!