Metal Shop Front
The metal shop front is quite useful for trading. The vendor can stand safely behind it without worrying about getting shot, as the glass is bulletproof. When the player on the inside and the player on the outside have put in items to make the desired trade, they both have to accept the deal for the items to be transferred.
As the Metal Shop Front has similar durability to a sheet metal wall, along with bulletproof glass, it can be used as a safe window to spy on neighbors at higher levels of a base.