Their production is efficient at 2-wide and the storage doesn't really scale up as well as production rooms, which are better at 3-wide. Medbays and Science Lab are good choices to make 2-wide (since each floor can fit two 3-wides, and one 2-wide). A good dweller will clear the emergency almost immediately because they're much easier. If you're trying to complete emergencies fast for an objective or achievement, use a 1-wide, level 1 room. Wider rooms and more upgraded rooms have harder emergencies (more rodents, higher hp, longer fires, etc). Make the room as wide as you want before upgrading, basically. Production rooms have higher tiers for example the power generator room that you have available early on is eventually replaced by the nuclear reactor. It's cheaper to make a room 3-wide, then upgrade, instead of upgrading your 1-wide, upgrading, and then trying to add/upgrade another 1 or 2-wide next to it to get it to merge. When planning your best Fallout Shelter layout you also need to consider: 3 wide rooms are more efficient in Fallout Shelter except for the Medbay or Science Labs where 2 wide rooms are preferred. When you upgrade rooms, it's more efficient with caps to upgrade merged rooms. Since all the 2-wide required rooms have already been mentioned, crafting rooms (and the theme research room) are required to be 3 wide.