With "who" as the subject, use third person singular (is /-s form). Who lives in this room? Who likes chocolate? If you use who with a "be complement," use the number of the noun: Who is that student? Who are those students? With "who" as the object, make the verb agree with the subject. In formal English, use "whom." Who(m) is he helping? Who(m) are they visiting?

To add to the previous answer: I believe the latter can be used if "who" is a relative pronoun. "My parents, who live in this room, are..." In that case the verb should agree with the subject ("My parents"). "Christy, who lives in this room, is..."

i live in this room!