Perform conceptual design of the operations of your local community library The library has books, CDs, tapes, newspapers magazines, etc, which are lent to library patrons. The latter have accounts, addreesses, etc. If a loaned item is overdue, it accumulates fines. Some patrons are minors, so they must have sponsoring by adult patrons who are responsible for paying their fines (or replacing a book or other item if lost).
Use the E-R approach. You can team up with ONE other person in the class if you wish.