Do Not Use Each Other's Things Without Asking. Not using each other's things without asking is one of the more obvious roommate rules. While some people are more casual about sharing, others are not. You have to learn what kind of person your roommate is and then act ingly.
A Roommate Agreement is a written contract between roommates that outlines their rights and obligations while living together. This agreement includes house rules, maintenance duties, restricted behaviors, and more. For a Roommate Agreement to be useful, everyone sharing the household must agree to it.
A flashback in the season three episode “The Staircase Implementation” reveals that the two characters met when Leonard applied to be Sheldon's roommate. That moment, we are told, was “seven years ago”, and the episode aired in 2010, meaning that Sheldon and Leonard presumably met in 2003.
A roommate arrangement is when multiple adults occupy a single unit together. In most cases, the renters are not related, but siblings and cousins can be roommates as well. With a traditional roommate arrangement, all roommates share a single lease.
It dictates what Leonard has to eat each day of the week, what TV shows he is allowed to watch, whether he has a girlfriend stay over, that he has to drive Sheldon everywhere he wishes to go, whenever he wishes. It even dictates when Leonard is allowed to use the bathroom.
It was the one titled The Staircase Implementation. He moved in with Sheldon in 2003.
My take is that at the time when he was interviewing for a roommate, he was just freshly starting out at his job so the rent was too expensive for him to afford alone, but as his work in the university gradually secured him a steady income years later, he earned more than enough to live alone, but he simply chose not ...
Sheldon and Leonard live together out of convenience not for financial reasons. Sheldon has said in the past that he wouldn't have a roommate if he could afford the rent. Penny on the other hand who lives alone on a smaller wage, is seen always struggling to get by, living paycheck to paycheck.
The Staircase Implementation - The Big Theory (Season 3, Episode 22) - Apple TV.