Just take a box, spray paint it silver, go to the hardware store or Radio shack and pick up some random computer/electronic parts and hot glue them to the box.
Cut holes for the arms and head completely cut out the part where your legs go so you can just slip it on over your head. Wear black tights and a black TURTLE NECK (if you don't wear a turtle neck then the box will rub your neck), wrap your arms in aluminum foil.
For a helmet just take a smaller box cur out the front so you can see and stretch some panty hoes over the cut out part, take two pencils and cover them in foil then stick them in the top.
Thanks to Eva (12) for this terrific idea!