It’s pretty well known how to create multi-story buildings at this point, but I wanted to try and compact that down a little bit so I used a different strategy.
Here’s the end result:
Basically, instead of doing the building with walls and all of the ladder scaffolding, you simply build floors on top of items. I’ve found dining tables to work pretty well. What you do is stack 3 tables (you could maybe do less than that but I didn’t want to clip heads off) and then build a floor on top of them. Important: BEFORE you start the construction of the floor, you should remove all of your tables or else they kind of get stuck and you can’t remove them very easily. Once the tables are removed, build the floor and repeat the process.
This example is a 5x5 footprint. You can place 4 tables and carefully place a floor across them that kind of overhangs the tables just slightly. You just have to get your mouse in the right spot to make it work. Also, sometimes you have to play with ladders on the outside just a bit to make sure your workers can pathfind to either add or remove a table.
You could maybe place this in a corner somewhere to help give the illusion of support. Not sure what the height limit is but several more layers should easily be possible.