I've made a cardboard box smoker http://www.instructables.com/id/How-to-Make-a-Cardboard-Smoker/?ALLSTEPS
before, but I wanted something a little more sturdy, so I made one out of a mini grill and some air conditioning ducts. The total cost for this project was $9 since I got the duct for $3 and the riveter for $6 at the flea market, and I found the mini grill in a dumpster (it's amazing what people throw away in rich neighborhoods). The hot plate belongs to my roommate, but you can use a charcoal or wood fire instead.
Step 1: Materials
1. A piece of sheet steel about 4 foot by 2 foot. Thickness isn't too important, as long as you can bend it into a circle. You might want galvanized or painted steel to prevent rust. I got my sheet metal by tearing apart a duct.
2. Mini grill, or a full-size grill for a larger-capacity smoker.
3. Rivets or screws to hold everything together.
4. Electric hot plate.
You will also need these tools:
1. Power drill.
2. Riveter or rivet gun.
Step 2: Build Process
1. Find the circumference of your grill to make sure the metal is big enough to make a full circle, then add a few inches for the overlap of the joint. Mine came out to about 4 feet.
2. Cut out the metal in the right size.
3. Bend the metal around a pole or other round object to make it into a cylinder.
4. Make sure that the cylinder will fit inside the grill, and that the grate will fit inside the cylinder, then tape the cylinder together.
5. Drill holes through the metal where the two sides of the cylinder come together and rivet these holes together to make a complete cylinder.
6. Add screws or rivets to hold the grate up inside the cylinder.
7. Add a coat of paint if you like.