I've made a testpiece as a template for the buildings, to get an idea of the simplest and most effective way to construct lots of buildings. To keep with the charcter of the BF:BC2 game,the buildings need to be able to represent various different levels of destruction. I've therefore built a central core, and added on the external walls as detachable sections, giving me 5 levels of damage (the fifth being total destruction).
The Core - 6mm MDF base - 6"x6", with a 3mm foamcard floor, topped with balsa that has been scored to represent planks. The internal walls are then glued on - internal wall height is 47mm, doorways are 40mm high, 30mm wide. External walls are 65mm high, to allow for a lip on the edge of the roof.
The roof is also 3mm foamcard, topped with plasticard for a corrugated look - the roof can be secured using magnets, to provide stability, but rests on the internal walls.
The external walls, are in corners, to allow them to stand up by themselves, with a small piece of wood to provide rigidity.
The final piece. Future buildings will vary in size and shape - some will have two floors - all will fit in a 6"x6" base so as to be interchangable.