This is complicated, but how would i go about creating a system that when i quit the game, it saves the map and loads it when i return, items on the ground, etc...

Not that hard sounding, but waht I want is that when people update it, I want the map to show the updates, new mobs, etc, but also show what WAS there last time they logged off. I need the map to only load for the host, and to save when the host logs off, and to save constantly (with the repops)