Does zone/room size matter? for example an open parking lot broken into a fewer zones having more open space to more quicker through (also allowing more zombies to horde the same space) Most buildings are broken down into the same size rooms (3 different sizes). Does this seem to impact the game if there is too much limited or open space?
To simulate, and play-test, a 'parking lot' with open space you could use tile 7B and place an open door on each of the 4 sides of the central building.
(assuming that's the kind of layout you were thinking of)