Styrene plastic would probably be the material of choice as it's easy to cut (relatively) and easy to glue (to other styrene parts and accessories). However, there are many other sheet brick pattern products available in vaccu-form styrene, resin, plaster/hydrocal, etc. so anything new would have to have some distinct advantage.
Disregarding styrene as a 'material of choice', and easily cut, it should also be able to be damaged for ruins, etc., thick enough for a scale wall thickness, and have interior wall surface detail, texture, etc. Various exterior brick patterns as well as stonework, ie., cut stone, field stone, with mortar or dry-fitted, etc. Maybe separate exterior and interior wall sheets and the individual modeller can vary and determine his own wall thickness. Just a thought!
