My one question: Will there be a variety in zombie damage against various materials depending if it is a weak, medium or strong zombie?
For example, i could imagine zombie nurse hitting for less than a football player, cop or biker, so having less power to damage stronger blocks. This could be incorporated in a manner that "weaker" zombies will deal 60% damage to metals, 80% to bricks/cement and 100% to others. Stronger variants could deal 90% to metals, 100% to bricks/cement and 110% to others.
Values can be tweaked in any way, but i know the mechanics are there, as i tweaked it in a modlet in A17. This could make a fine addition in general, making early game a bit easier, but late game harder (stronger Zs more easily messing up the base).