Mastering AI (top down zombie)

Mastering AI is the hardest thing for me.

• I have a building in the middle of the map.
• I want the horde of zombies to know I am in the building, but they're not sure where in the building I am. (this is to prevent zombies going up and down when I move around on the inside of the building)
• I need them to scout around the building with some attacking the doors and some attacking walls and some wandering some more.

How do I make AI with pathfinding walk around the building and try to find a way in?

Give different zombie types different 'jobs' or destinations, or possibly 'states' if you want all zombies to do all actions. Then assign some with destination of the door, some with the player as the destination and some with random destination. Set the building as a solid obstacle so that they will try to find a path around it to reach their given destination.