For this years science fiction convention I decided to go as a cyberman from Dr. Who.
specifically, the cyber controller from the episode Earthshock.
It took about 2 weeks to build the costume and about two days to make the gun.once it's done it is reasonably light and easy to move around in.
To make it you need
Silver tape (the kind that you use on air vents and the like).
A plastic bottle, 3.5 inches in diameter
Red and black tape, or paint it isn't used that much
A silver jumpsuit and gloves (or if you can't find that buy some coveralls and spray paint them silver like I did)