When you go into the boss that hangs from the ceiling walk straight in and kneel down under him.
Then what you need to do is then shoot the glass cage and let the walker out.
He won't attack you when you are standing here then kill him where you are dont move because if you move the ceiling beast will kill you.
After the walker dies two little guys will pop out kill them then start shooting the ceiling beast he can't hit while your shooting him.
Wear him down into the red zone then use your flame thrower twice and run like hell around the room this should kill him, if you follow all the steps as listed don't try to push your engineer in their because it he dies then you lose.