On the record label level is where I got mine. Destroy everything and pick up everything on the first floor, boarding windows an doors as you go. I kept the zombies away from the main room and the room with the stairs. Then board up Mike in the bathroom by the stairs. Once there is a good collection of zombies, start putting the construction hat traps on the windows in the main room and then the doors in the main and stair room. By the time I got the last door done, it popped.