I think the best fenced building is the Central Bank in East Avenue. Grilled 3 inch bars used as walls, 20 feet in height thus allowing you clear visibility in case you want some target practice on zombie heads. Not to mention the presence of a 30 feet drop zone straight to a wide trench that can fit a huge bus. This is then followed by another grill fence. It would have been nice if the only entrance and exit is a draw bridge.