Mutant Apocalypse: My Invincible Mechanical Farm

Caleb has a farm on Sunset Hills that he put together with a welding torch and a harvester he modified. He was an elite soldier before any of this, and when the mutations started and the world came apart he activated the Doomsday Bunker System. The greenhouse he works in is bulletproof. He grows wheat that resists the virus, and he eats hot meals in there while everyone outside is dealing with zombies and with the food running out. He stockpiles grain, puts up walls, and brings in survivors who are good at something. The farm turns into a fortress of steel over time, with heavy guns on the walls and Titan Mechas standing in it.