Paper Prototype

My game will be a strategy, tower defence type game. The game will discuss diseases, and preventions of certain ones. Diseases that cannot be cured, will not be able to in the game, and fatal diseases will eventually kill you in the game, just as they would in real life. The main goal is to keep your character alive, and make it through as many rounds as possible. The main activity is to strategically place vaccines, and antibiotics to destroy incoming diseases before they reach your characters face. The only problem I think we would face in creating this game would be the diseases coming down at your character randomly. We would like for each round to last around 1-1 1/2 minutes, and don't want to have to code each of those seperately. A random code would be AWESOME!