If you want to become a game designer then you will need to gain the appropriate education. While some game designers have gained stable employment by simply showing their portfolio, this situation is becoming increasingly rare. Nowadays employers want to see where and what you have studied and where you received your degree. Of course, they will also want to see your portfolio which means working on games in your spare time or as study projects is the best way to present yourself to an employer once you've received the proper education.