-Game Idea
Make a management game where you are trapped in a city's hospital, suburbs, store, office, etc. And have a handful of people that play a vital role in survival. You have to retake the entire city, scavenge for supplies, recruit most of the remaining civilians and give them roles like Building, farming, scavenging, researching, and healing/being doctors.
Make it an option to make squads so that you can be like, Oh I want to send Alpha Squad to the overrun hospital to gather medical supplies! or I want Bravo Squad to secure the highway so we can start a supply route.
And one last thing, make it so there are neighboring settlements that you can raid/alliance/trade/save/or conjoin them into your own. The Currency for trade should be coins :P
Nice Game!
Some Ideas I would like to share are custom leaders/generals that you can create and battle other players on a huge map, kind of like RISK, except for the custom leaders :P