Establish House Rules via a Protocols and Procedures Manual with a Sign-Off contract a copy of which is kept by the coop's lawyer, a copy of which is kept in-house, and a copy of which is kept by the signee.
Draft a formal agreement on per capita expenses such as: rent/mortagage, utilities, baseline contribution toward repairs, insurance, and meal plan, if applicable.
Draft a formal agreement on living space designations. For example, a couple that is expecting a baby might get one of the larger rooms. A single student who does not expect to have sleepovers, might opt for the smallest room. A post-doc who is in the throes of publishing might need a room with its own bathroom more so than a couple who is expecting a child.
Draft a formal agreement on chore schedules (e.g., rotational schedule, monthly, weekly, etc.)