To tie into Fallout 4 and the institute, I suggest the Robotics Lab and a series of Modification Labs. In the Robotics Lab, dwellers can build synthetic dwellers and in the Modification Labs (one for each stat in S. P. E. C. I. A. L.), synthetic dwellers can be upgraded with stronger parts and have their settings fine tuned to increase their stats. Essentially, these rooms will be synthetic alternatives to the living quarters and the training rooms. I'm not proposing a dweller cap increase. Instead, Living Quarters and Robotics Labs would share a cap of 15 units (the current living quarter cap) so you as the player can choose if you'd like to have no synths, a mix of organic and synthetic dwellers, or even, later in the game, switch over and have a completely synthetic vault by killing off all of your organic dwellers and replacing all of the Living Quarters with Robotics Labs. To create new synthetic dwellers, simply staff your Robotics Lab with dwellers, the higher intelligence, the better, and they will work on building synthetic dwellers. The mechanic will work just like the radio room for calling in dwellers from outside, with a chance for success, not a guarantee, but instead of the synthetic dwellers running to the door from outside, they simply spawn inside the Robotics Lab. To offset the relatively lower population growth rate of the synthetic dwellers, they do not have a childhood phase. They are built as fully functioning advlts, ready to get to work immediately whether that be working in a production room, exploring the wasteland, or going into one of the S.P.E.C.I.A.L. Modification Labs to have their stats upgraded. Lastly, instead of requiring food and water, synthetic dwellers require power so the vault's power consumption will increase for every synthetic dweller that exists but that also means if there are no organic dwellers then the vault needs no food and water production rooms.