EMPLOYEE WAS HANGING VENT TUBING IN THE #3 ENTRY OF THE 2 RIGHT SECTION. A SHUTTLE CAR SNUBBED IN SAME ENTRY HAD A WORN SPOT IN OUTER JACKET THAT LET LEADS CONTACT METAL SNUB. THIS RESULTED IN THE WIRE MESH ON ROOF BECOMING ENERGIZED. WHEN EMPLOYEE WENT TO HANG METAL ""DOG CHAIN"" ON ROOF, HE WAS SHOCKED. EMPLOYEE REPORTED MOMENTARY LOSS OF CONSCIOUSNESS.