You can use most types of building materials to make the casing of a tag gun. It all depends on if its suitable for the design you have choosen.
Most of my guns use a combination of the materials, using the most suited to the paticular function.
There are 3 common materials used though.
Personally I dont like to use wood for the main body shell as strength to size/weight it isnt very good. It does have the advantage that it is commonly available. Many of the earlier custom guns were made of it.
Its very good for making curved parts though like grips. It is also easily shaped, especially if you use MDF (Medium density Fibreboard).
A great material for making tag guns out of. It is lightweight and easily cut and shaped.
Especially useful as there are many diameteres of pipe available. We use it quite alot in the making of lens assemblies.
I personally think guns made primarly out of plastic are a bit light (I like some weight to a gun).
Many custom guns have been made from plastic but more complicated shapes suffer from a lack of strength. That aside I have seen some VERY nice examples made from this material.
Now we come to my favourite material. I use mainly aluminium for my body shells as it is lightweight yet strong and also still fairly cheap.
It also doesnt rust like steel and is almost as easy to cut and shape as plastic once you get the hang of it.
A good metal stockist will be able to supply aluminium in various sizes and shapes of extrusions as well as flat sheet.
When these different shapes are combined you can make some really nice gun shells that are very strong.
The most useful extrusions are [ shaped channel in various widths and depths and sheet.
I tend to use channel with a 3mm wall thickness as this gives a very rigid 'spine' to the weapon and is thick enough to drill and tap a threaded hole.
Onto this spine I then attach all the various sheet sections I have made until the shape of the gun emerges :)
I'll go into more detail in the Construction techniques section.