I have no map skills... just photoshop skills so i give an idea instead...
Here is the idea: A church map, dark gloomy halls and all, and there are 2 stories... humans on top, aliens on bottom, and there is a small garden outside. Should be no bigger than 1.5x the size of ATCS or so... maybe 2x... just an idea for people who wanna challenge themselves with something new...
If you wanna get an idea... KillingFloor has church pictures / videos, and let me tell ya... this would be an awesome MAP!