A barricade is an object used to create a barrier. The most common in zombie films are made of 2x4s. However, it could be made out of any heavy object. A good example would be a metal desk or wooden chairs. The stronger it is, the less likely zombies are going to break through the barricade. It is best to have barricades if you are going to spend a long time in a building or section of a building. Some buildings, such as hospitals or police stations may be too large to completely barricade. Instead, barricade a wing or section off more heavily. Remember to have an escape route however, but make it one such as an emergency ladder so you can retract it to keep zombies and raiders out. Theoretically, one could barricade him or herself alone in a room with no windows or small, high up windows with ample supplies or a farm and water source and never leave. However, being confined in a small room for so long would likely drive most people completely insane. If you have the resources, try and give yourself a few rooms to move around in, but don't overdo it.