On the multiplayer level damination set your health to 400% w/ shields. Pick up the rocket launcher and find the room with green lights all over it. Go to the corner where the sun is (the right one from facing the stairs. Throw a frag grenade at your feet, then jump up and shoot a rocket. If done correctly it should launch you up on top of the level. From there you can walk on top of the roof of the level.
If you cannot do it from the green room try the room next to it (it is attached to the room with the active camo.) Go on the pipe and rocket jump (jump and shoot at your feet) up to the top of the level.
This egg has worked numerous times for me and should work for you...good luck