You can use the following example as a template for building your own game. It's based off the classic arcade game "Asteroids", you may however modify it into a completely different style of game.
You may also choose to start your game from scratch, but be aware that this is more challenging. Your code must still be structured and make use of Object Oriented principles.
At minim your final game should include:
- A concept and a visual theme
- Original graphics
- Sound
- Appropriate start, play and game-over screens
Helpful Links
http://www.lostgarden.com/2006/10/what-are-game-mechanics.html