Amuro

Construction materials really depends on your style of running (hard or delicate) and the extent of power and transmission you would like to use.

Styrene is easy to work with and if you go this route, keep everything as light in weight as possible i.e. no metal parts except for perhaps aluminum in some places. Do not use powerful motors or gearboxes that may twist your Styrene model too much, metal tracks is out of the question. Light weight plastic models can be made rather cheaply and be sturdy and nimble on the battlefield and easy to service, just avoid getting hit by a heavier tank!

Metal is the best construction material for larger (heavier) tanks with powerful motors and metal gearboxes. Any metal wheels, tracks or suspension sysytems will almost always necessitate a metal chassis, although the upper hull and details are fine as plastic. Metal will be highly resilent and can take some punnishment for accidents and rough driving but the weight is hard on the mechanical systems as well so design that portion well.

As a caveat, if you have the plastic mold capability, then high impact (unbreakable) plastic such as the Leopard is made is the best combination of weight and ruggedness!