I recently had an idea for a shooter game.

The idea is that you are a military-type, and there's been a zombie outbreak. You have to go from town to town, and rescue as many survivors as possible while eliminating as many zombies as possible within a time limit. The number ofzombies you kill dictates the number of zombies in the next city, and in order to win the game, you have to get that number lower than ten percent of any given city's population. That's basically it, but there's a few more factors.

If you manage to kill half the zombies in one city, the amount of time you had left as well as the proportion of killed to living zombies is used to determine the proportion of normals to zombies in the next town.

If you rescue over fifty percent of the population, you gain a small bonus; an extra magazine of ammo when you start in next city, a grenade when you start in the next city, something minor but useful.

If you rescue over seventy-five percent of the population, you gain a medium bonus; a magazine of armor-piercing rounds when you start the next city (one-hit kills), two grenades, extra time in the next city, something very useful, but temporary.

If you rescue all the survivors in a city, you gain a permanent bonus; an extra slot for grenades (normal amount is two) as well as grenades to fit, more time in all subsequent cities, something that is very good and has lasting effect.

Not all zombies will be stereotypical slow limping zombies, most will, but some will be fast, some will be extremely strong, and some will be very resilient (more HP).

The game has almost infinite replay value; every city will be randomly generated.Yes, this is basically leading up to one of my random whatever algorithms, but there's a twist! I'm stuck. I've hit a wall. I'm confused. I need help.

I can make worlds, caves, and islands, but the more man-made cities have me stumped.

I had the idea to make it be filled with 3*3 block cells, which will be selected based on their surroundings from a huge bank of different possible layouts for the cells, but I just can't seem to figure anything out about how it might work beyond that, and I can't think of a way of making the program know which cells are compatible with others. Since it's a grid, too, there might be the problem of having almost identical city layouts due to less options for the cells.

Can anyone help, by expanding upon my idea or making up their own? Has anyone heard of a system that can do this? Any sort of help would be nice.