Re: Can't ask certain sims to be roommate.

The game will not let you ask these types of sims to be roommates by design (the Ask to be Roommate option will not show up at all):

• University professors
• Robots
• Sims who are already roommates at another location, such as university housing

For everyone else, the Ask to be Roommate option should be available (but they won't necessarily accept - for example if they already own a home or live with other people).