Here's a one way window where on one side you can have a view of the other room while on the other room you cannao t see the other room.It's good for daethmatdh maps because you can shoot the enemy while he can't see where it's coming from.
here's how to make it:
1. Make two rooms
2. Make an opening for the onw way window
3. Make a brush
4. Texture the brush so that one side has a texture while the opposite side has a null texture.
UPDATE: I added glass.
I turned the ratings on so you can rate how good is the example.