Hey there-
What kind of "smoker" do you want? This could mean many different things to many people.
First off, cold smoke, or hot smoke. Cold smoking is where you cure the meat first, then subject it to a cold temperature (often around 90 degrees F or so) smoke for a long period of time. Bacon is a good example of a common item that is cold smoked. Hot smoking is where you subject the meat to a much warmer temperature, though not quite warm enough to actually cook the meat. Smoke is added to the process as a flavoring. A simple design would use wood or charcoal to create the heat, as well as the smoke for flavoring. More complex designs use an electric element, or even gas to create the heat, and there is usually a pan that can be placed directly over the heat source for wood chunks to smolder and creat the smoke, but the heat that does the work does not come directly from the burning wood.
Secondly, a lot of people refer to a barbecue as a "smoker". Also, a lot of common grilles are called "barbecues", I'll explain. A grill is a device used to cook meat over a direct heat source. Even though they are often called barbecues, a weber kettle grill is not a barbecue in the technical sense. The meat is cooked directly by the heat source. You can almost barbecue with one, if you really know what you are doing. A barbecue cooks meat much slower with an indirect heat source. Barbecuing cooks the meat at a temperature ideally just a bit below the boiling point of water (so the juices don't simmer out, but the meat doesn't get dried either). Because the slow cook method often involves the burning of wood, and the smoke is carried along with the heat and also provides a lot of flavor, these barbecues are often called "smokers". The two most common designs are what is commonly known as a "water smoker", and an offset firebox barbecue. A "water smoker" is a fairly cheap design that can have it's advantages, however you must really know what you are doing to use it effectively. It can be very versatile, useable as both a hot smoker and a barbecue if you know how to manage it.
Finally, a few people say "smoke" when they really mean "dry". If you are thinking of jerky, this applies to you. Jerky is often said to be smoked, really it is dried, though it may be subjected to smoke, for flavoring. My favorite jerky recipe I do in my oven, set to the lowest setting, and sometimes I even leave the oven door open a bit. Jerky can be done in a hot smoke method, but most common recipes just use a food dryer, oven, or even outside air on a warm sunny day.
So, do you want to cold smoke, hot smoke, or barbecue? There are lots of do-it-yourself designs for these available, but you must first understand completely what you intend to do to the meat, because the design of the smoker has a great deal to do with the quality of the end product. Very minor design differences often make the difference between wonderful meat, and lousy meat. Understanding how temperature, airflow, heat, smoke, etc. all work together will help you choose a good design, or perhaps help you make your own alterations to an existing plan.
Sorry if this is a bit long, let me know if you have any questions. I'd like to help, but I need to first understand exacly what it is that you want to end up with.
