An offset smoker is comprised of two parts - the firebox and a cooking chamber. The firebox is the part where the fire is taking place (duh), which also has a fire vent and an access door located on top or to the side of it. An offset BBQ smoker has a small hole that connects the firebox and cooking chamber together so the smoke can be transferred faster. The cooking chamber usually has the same shape as the firebox but it is bigger with some grillwork inside to hold the meat and it also comes with a lift door and a smokestack.
Vertical Water
The cheapest option on the market is definitely the vertical water BBQ smoker which is also the one that requires the least amount of cleaning and by some, it is more efficient than most smokers. They have three different compartments put into one. The part closest to the ground is the firebox which is basically a metal bowl that has a grate at the bottom and in this case, there's also a perforated metal collar. In the middle, there is a water pan that makes this system different from the others. At the top is the smoking chamber which has a lid instead of a lift door.
Drum
This is the simplest smoker as it has the firebox and the chamber in one whole part which also makes it the easiest to use. If you are a heavy DIY-er there are kits that will allow you to assemble one yourself. Much like a vertical water smoker they also have a lid but they do not make use of water instead, charcoal is the supplier of smoke. They have a vent on the top for the smoke to come out and one on the bottom to let heat in.
Box
These smokers have a vault-like design with the chamber being on top and the firebox on the bottom of it. They are similar to a vertical water smoker in which the smoke rises up to the meat making it ideal for conserving heat. The firebox or the source of heat is usually powered by electricity or gas when it comes to these smokers and they don't have a vent as there isn't really any smoke. In fact, the better insulation they have the better they are at "smoking" the meat.