Fallout Shelter rooms

There are a total of 20 available room types that begin at level 1 and can be upgraded with caps to a maximum of level 3. Rooms can also be merged up to two times by placing an identical room of the same tier next to it. Generally each room can facilitate two dwellers. Merged rooms accumulate up to 6 dwellers. Production rooms require a specific S.P.E.C.I.A.L trait to run, while training rooms increase the traits of the selected dwellers.

Room overview
The cost of each new room is dependent on the number of those rooms already in your vault. E.g. Your first Med Bay is 500 caps, while your second Med Bay costs 600 caps, and so on.

Production Rooms
Production rooms yield one resource, except for the Nuka-Cola bottler which produces food and water. Production time is dependent on the number of dwellers and their trait level for the room's required trait. Once a room has produced a load, they do not produce any more until you collect the resource. Depending on the luck of the workers, collecting the resource may also give a sum of caps.

These rooms can be driven to produce resources quickly. Depending on the probability given in-game affected by the luck and the traits of the workers, the room can instantly yield resources and a number of caps equal to the percentage of the chance taken. A failure on the action leads to an inevitable incident in that room, either fire or radroaches.

Although it is not visible in their SPECIAL stat bars, wearing outfits that raises stats beyond 10 increases production nevertheless.

Training Rooms
These types of rooms raise one of the traits for the dwellers stationed in it. Training time depends on the dwellers' current level, the room level and how many occupants are in the room. Going from level 1 to level 2 takes a few minutes while going from 9 to 10 takes up to 20 hours. Dwellers train faster with more dwellers in the room.

Other Rooms
There are three rooms, which are neither production nor training rooms: Vault door, storage rooms and elevators.

The vault door can hold up to two dwellers as initial defense. It can be upgraded two times to strengthen the door against raider attacks. Obviously the vault door can neither be deleted nor built nor merged.

Storage rooms are neither productive nor training rooms. They simply extend the number of outfits and weapons you can hold in your vault. Although storage rooms have a S.P.E.C.I.A.L trait associated (Endurance) dwellers have no effect in these types of rooms. You might want to use storage rooms to stop your dwellers from wandering your vault and have a place to quickly find them though. Note that Storage rooms do not extend the capacity of Stimpacks or Radaway. To extend the storage capicity for these items you have to build or upgrade Medbays or Science Lab respectively.

Elevators connect the different levels of your vault. Note that your vault may grow downwards only. In contrast to all other rooms they are much smaller, roughly one third of a normal room. Elevators cannot be upgraded.

Merging
A maximum of three rooms can be merged to one bigger room. Rooms should be merged as early as possible because merging is beneficial in multiple ways: Upgrading merged rooms costs less than the cumulative upgrade costs of the same number of unmerged rooms. Also merged rooms are more productive and effective than the same number of unmerged rooms. For production rooms this means they produce more items/energy/food/water. For training rooms this means the training times are reduced.

Room Layout
In the current design of Fallout Shelter the first floor of your vault can hold five rooms (whether merged or not does not matter). The second floor can hold seven rooms. All following floors can hold eight rooms. Each floor can also hold two elevators. Building a third elevator will take up space of one of the rooms so it is not recommended. These facts results in a standard vault layout, where the elevator rows [E] could be moved to build two blocks of three rooms and one block of two rooms, as shown by this example: