This is the UDS (Ugly Drum Smoker) i built a few years ago. These are really inexpensive to build, economical to run and have lots of cooking area.
1 Oil Drum preferably unlined.
9 30mm long M6 Stainless Steel Bolts with Washers and Nuts
2 57cm Cooking Racks, you can get these from Homebase around £7.00 each
3 Handles, 1 for the Lid, 2 for moving
Charcoal Basket, i used an old Beer Keg cut down.
Air Vent, £4.50 off eBay
I Use a Pit Controller for air flow management, but if doing it manually you will need, (all fittings from ScrewFix)
3 22mm Ball Valves 36.89 each
3 22mm Tank Connectors £3.65 each
3 22mm Elbows £3.81 pack of two
3 Pipe Clips £3.55 pack of five
1 lenght of 22mm copper pipe £12.59
If you have all the parts to hand, this type of build can be completed with in a day.