Suggestions
Security Room, dwellers asinged to this room will patrol the level they are on and will respond to any threats like Raider attacks radroaches and mole rat on the level they are on and above and below them only. Dwellers with high Strength and Perception will do good in this room.
Maintenance Bay, this room will allow you to add a new mechanics of game, rooms will be damaged during attacks,fires and everyday use with the help of the mechanics they will patrol the levels above below and the one they are on, fixing the rooms as they become damaged, also at 50% health Mr handy automatically dock in the maintenance room to be repaired so you can drag them to repair them sooner, the room will have one docking port per size. (Max 3)
Dwellers with high Perception and Endurance will do well in this room.
Exploring, add a mechanic that allows you to set a time for exploring as well as an automatic return if the dwellar runs out of rad away or stimpack.
Added.
Traps, like mines or barbwire to help defend the vault door, tho theese reduced the likelihood of people coming to your vault.
Also log or rock trap up the mountain or even add a look out post to see when a raid or attack is coming and issue a power down command to have a chance to avoid it.
Added two.
Command room. Four dwellers ony two rooms large, room adds a 2% (per room) to the chance of finding caps and items from exploring, at level two you can have a team of two dwellers explore as a team and Max level three, each room can only support two teams of three each.