A roommate is a kind of NPC available in The Sims 2: Apartment Life, The Sims 3: University Life and The Sims 4: Discover University. A playable Sim can apply for one or several roommates, who live in that Sim's household and pay rent. This term can also refer to Sims that are living in a household with another Sim, but is not in any way yet related with each other.
The Sims 2: Apartment Life
In Apartment Life, roommates are only available for those who live in apartments. They are treated like pets - selectable, but not controllable, unless the "boolProp controlpets on" cheat is used. Roommates have jobs and go to work, but their salary will not contribute to the family funds. Their only contribution is to reduce the rent price.
A roommate can be found by using the newspaper or computer. Sims can also place an ad over the phone. Occasionally, Sims will receive phone calls from social group townies who want to become a roommate. The number of roommates available by newspaper and computer will decrease if the searching Sim's reputation is worse than Dubious Delinquent. Only social group townies are available as roommates through the newspaper or computer. Sims can ask any townie to become their roommate if their relationships are high enough.
The Sims 3: University Life
Roommates arrive to a household at the exact same place and time, and will appear to be jumbled together.
Roommates return in University Life. Roommates are Sims that share the player's family home and expenses, but are not part of controllable members.
Sims can obtain roommates by using their smartphones. Once a residential lot is filled with uncontrolled roommates, a new "Roommates" option appears when interacting with the Sims. Sims can "Mooch", "Ask Roommates to Clean, Fix Broken Objects or Make a Meal", and "Dismiss Roommate". Dismissing a roommate will remove them from the household, and they will be replaced with another one. The roommate service can be disabled in the phone Real Estate option, which will prevent roommates from being replaced with another one. With so many Sims around the lot, it will probably be good idea to either lock the doors or to claim a bed.
If a Sim builds up a strong romantic relationship with a roommate, Sims can eventually propose and get married. When playing in the home world, any roommate the Sims marry will become the member of the household.
With the exception of work or grouping up with a controllable Sim, roommates oddly never leave the house on their own. They can be seen in map view as part of the player's household.
In Sims University, they automatically live in dormitories and Greek houses.
The Sims 4: Discover University
Roommates return in Discover University. They automatically show up in university housing, provided there are enough beds, but Sims can also rent out their homes, apartments[CL][EL], or residential rental units[FR].
Getting roommates
Sims can get roommates by placing an ad on their computer or phone. If there are no extra beds on a lot, the option to put out an ad will be grayed out. There can be up to ten Sims living on a lot, including the playable household. So, for example, there could be a full household of eight playable Sims and two roommates, or one playable Sim and nine roommates.
If a Sim places an ad for roommates, potential candidates will randomly visit throughout the day (or the next day, if the ad is placed at night). Sims can then get to know them before accepting or rejecting them as roommates. Once all beds on a lot have been filled, the ad will automatically be taken down. However, the ad can also be manually removed. It is not recommended to buy double beds for roommates if space is a concern, since a roommate claims an entire bed when looking for somewhere to sleep. This prevents others from autonomously claiming the other side of the bed. This recommendation doesn't apply to bunk beds, though. Roommates will claim the top and bottom bunk separately because they are technically two separate beds.
Roommate behavior
Roommates will pay rent if the player's household owns the lot.
Roommates are completely uncontrollable NPCs, and will take care of their needs without the player's input. They will leave at times during the day, either to go to work or to visit other lots. Each roommate is assigned a hidden "archetype" that determines how they behave as a roommate. For example, some will litter more, some will often invite over their significant other, and some will throw parties. Playable Sims can scold roommates for inappropriate behavior, and can dismiss them at any time. If the player's household owns the lot, roommates will pay rent to them.
A roommate deciding to come along to a community lot without being invited.
Roommates may decide to tag along if the player takes the playable household to a community lot. Roommates may also leave notes around on the floor with written complaints for the player's Sims to read. The player can then have their Sims confront the roommate about their notes, which will decrease their relationship.