Here's a cool idea(s): You could build a junkyard with a lost mine below, and make a Chit hunt. OR you could make a build with one big endurance quest (kinda like Paper Mario's pit of 100 trials, only with about half as much rooms and with counters and checkpoint traders.) I also thought up a mission.
Rooftop Rush
Objective: kill as many zombies as you can! Kill 1 zombie=.2 Chits 5 kills=1 Chit. Face off against normal, dog, slow, and fast zombies on top of a large building. You are armed with only a gun, two medkits and a propane tank, so use them all wisely! *this mission belongs in infected city.