Persistent world with UE4 (not an MMO)

And that’s something I totally do not understand. How can I know what to spawn? Let’s say player adds 20 walls and 5 doors to map. I can save these, but how to load such state? Do I need to store separately how many walls and doors I have and spawn them? How to actually “assign” data from SGO?

It’s surprising that SGO is easy on saving part, but loading part gives such hassle and that’s only considering a single player game. Hard to imagine that it would be any easier with multiplayer.