Sheldon: I need somewhere to work in the evenings. You have a space you aren't using. Just take a look at my proposal.
Penny: (groans) What is this?
Sheldon: A rental agreement. I will only use the room for work. I won't sleep here, I won't eat your food, I won't even use your bathroom.
Leonard: So you can just walk in any time of the day or night?
Penny: Well, he does that now. At least this way we'll get paid.