There are many ways to make known the purpose of the tanks which was built simply by examining the weapons with which the tanks were equipped. Some of these weapons include assault guns, multiple missile tubes, flame throwers and single round turret mounted guns to name but a few.
By making sure that the model you are assembling has been properly outfitted with the correct weaponry you will go a long way toward making sure that it is accurate. If you are building your models to represent their nationality then you will have to consider several different factors. For example if you have decided to build a Russian T-34/85, which was first produced in 1944, then you must decide what era it is coming from.
They were used in WWII and would have been outfitted with either Polish or Russian markings. They may also have markings showing their use in many of the more modern campaigns in which they were used such as North Korean (1950-51), Vietnamese (1970-72) or even Yugoslav (1991-94) markings.
Many good model builders will make sure that they have recreated the tank very accurately. This can take a bit of research on their parts, and many times they will display part of the material that they produced during their research alongside the model. There are some tanks that have not been produced commercially for model builders.
Those that find that this is so may opt to scratch build their tank. Scratch building is a process by which a model builder will use sheet plastic to create a model from a set of pictures instead of using prefabricated model parts. This can be a bit time consuming and can take a good deal of trial and error, but it can also produce an excellent looking model. Model builders that choose this method will sometimes have to add a couple commercially built parts such as a machine gun, but this in no way effects the overall outcome of the scratch built model.
If you are considering taking the scratch built route then make sure to do the proper research so that you can get your accessories and decals correct. If you do so then you will be able to create the most historically accurate tank possible.