A PHP/MySQL design, like any other web / database designs cannot refer to the vacuum! A work of this type could be tiresome, and sooner or later, it would use up all your energy and motivation. You should look for a practical idea. Look around yourself; take a notebook and go around, to shops, libraries, ... Look for any thing you could model by database and cyberspace. The ideas would surround you very soon, and you will find it difficult to pick the best.