You will get more rooms of the same type as you level up your shelter. Most rooms can be merged to get a bonus (10% at 2 rooms, 25% at 3 rooms). Rooms need to be the same level to be merged together and can't be split once merged. Elevators can't be merged but act as if they are preventing you from moving or removing them. So once you place elevators next to each other horizontally, they are stuck in place.
The following is a list of all the rooms that exist currently.