Wood:

Wood is a very easy material to cut. This means that it is quick to use, but can be easily broken. There are a few types of wood: manmade wood, hardwood and softwood. They are both used for different things. The hardwood is more expensive but is a lot stronger. This means it can be used as structural instead of decorative. Whereas the softwood and manmade wood are usually a lot weaker and cheaper; therefore used mostly for decorative.

Manmade wood, like MDF, is made up of the byproduct of wood production compressed. This means it does not have a grain and can be cut easily. This also means that is cannot warp and is very smooth. 

Metal:

Metal is the strongest of materials used, but is also the most expensive. Metal can be bought in sheets, poles or rectangular cylinders. Although sheets are rarely used due to the high cost for little added benefits, the other two are widely used. The poles are always used as legs in steel deck as they need to be strong to hold up the deck. They are harder to cut than wood and need a grinder to cut them, but worth the extra effort to ensure a safe stage. The rectangular cylinders are used as major structural work on pieces of set. They are used because they are very strong and have flat edges to attach wood. They come in many different sizes, so that you can save money if a really wide one is not needed.

Polystyrene:

This is the weakest of all the materials, but still very useful. It can easily be cut or carved using a hot element. The best property of this material is that it is extremely light, weighing barely anything due to the high air contents of it. It is also kind of cheap for the amount you get, which means that you can build large three-dimensional elements with it.