To build a homemade smoker, you will need an old barrel or large metal container, a grill grate, charcoal or wood chips, a thermometer, and some basic tools. Start by cutting a hole in the bottom of the barrel to create an airflow vent, and then cut a larger hole near the top for the smoke to escape. Attach the grill grate inside the barrel, and then add a separate chamber for the fuel and smoking wood. Install the thermometer to monitor the temperature, and seal any gaps or leaks with high-temperature silicone sealant. Finally, start a fire with charcoal or wood chips, and add your meat to smoke and cook to perfection.