If you want to start smoking food outside ... sheet of metal. But a smoker does it much more efficiently and over a period of five to 12 hours until the meat generates a thick 'bark' or crust ...
They roll in a big cart of meat, turn it on, and electric heat warms ... BergenNorth Country at Work: Smoking meat, from the chimney to a commercial The smoker fits about 300 pounds of meat.