Rounds 1-5 stay in the first room, there are 4 windows and 4 people so it should be fine.
Rounds 6-10 open the bottom door and move through to the power, have everyone hit the box, then have 2 people watch the staircase and 2 people watch the window and the ledge.
Rounds 10+ move to the Phd flopper area, atleast 3 people need to buy flopper, then have 1 person on the widow upstairs and 1 on the window in the room, the other 2 with the best guns should be flopping off the main stairway one right after the other.
If you get in a bad situation use the lander then go back and do it again.