What are the rules? What materials do you have? How about tools- soldering iron? About minimum materials needed, " tin" can, wire coat hanger & 1/4 lb # 22-24 wire.
Don't build the "mercury motor" in this PDF: http://www.vintageprojects.com/science/5-motors.pdf as it will cause the EPA to have a conniption fit. I don't know where you could get ahold of that much mercury anymore nowadays anyway.
Mercury procurement: Just cut off end of about 100 8 ft. flourescent tubes and collect the mercury- turned in over an oz. ' used to use mercury to make low noise rotating contacts.