I like your idea and it doesn't seem hard to do. I also have an idea. As much as I think zombies have been done to death, I'd like to see a zombie simulation game. You start out in a metropolitan area at the start of the outbreak. You will have to manage your character's hunger and water needs and you may pick up other survivors who can lend you a hand but for whom you will have to do the same. Your survival strategy is up to you. You can roam with a small band or try to set up a bastion survivor community. You can roam the region freely. The longer the outbreak persists however, the worse the situation in the city will become. The game will push players towards holing up someplace, either in a fortified building, a courtyard walled off with shipping containers, a gated community, an abandoned house in the city or country side or maybe even a supermarket or mall you name it. Resources are finite wherever you go and you can order your survivors to do tasks like wall building, tunneling, item repairs or farming. You would have to keep everyone fed and hydrated while managing the growing zombie moat outside your walls with the idea being a focus on anti-zombie fortification and survival through minimizing exposure. Of course emergencies might occur like crop failure due to a lack of knowledge, an early cold wave that upsets winter heating plans or an outbreak of disease that would require you to plan sorties out of the fortress.
