In the following tutorial I cover all the aspects needed in creating a map change within a L4D editor. Perfect when creating campaigns. The tutorial is lengthy and comes in 2 parts.
1. Entity tool and place a prop_door_rotating_checkpoint prop. Name it checkpoint_exit.
Also set body = 1 and spawn position = closed
2. Make sure the exit sign on the door and the lock hatch faces into the spawn position.
3. Insert info_landmark into your spawn room in your room, close to the ceiling.
4. Create a Safe House location.
Insert prop_door_rotating_checkpoint entity into the safe house's doorway.
5. Make sure the picture of the house on the door is facing out, away from the safe house room.
6. Place info_landmark and
7. Create a brush with no_draw texture on it and surround the inside of your safe house room with it.
Select the brush and press CNTRL+T. Tie to brush and set class to trigger_level_change.
New Map Name: your next map name that it will change to.
Landmark Name: landmark_B or the name of the landmark that is inside your Safe House.