My biggest build is a LOT higher than 5 floors without any cheating. It took over a month!
The biggest thing cheaters do are bypassing stability and allowing unusual rotation of parts. There are other things, but those two are the main ones as I understand it (?).

here is my biggest castle. Its unlivable -- too much stairs up and down to access single purpose rooms like kitchen, bath, crafting, storage, resting, trophies, ... way too many rooms some are empty but it was fun to build and I use it as a remote base. What you are seeing is +- 8 (that is, I dug a flat area down to bedrock, and started there with a terrain ring. The terrain ring goes through the inside of the outer walls on the lower levels where it is fatter. That gives me multiple stories of basement. Then above the neutral level, where it gets narrower, its good old fashioned iron supported normal (pre marble) rock, with a wooden top. Several rooms have high ceilings because why not, but if you sliced it at 3m tall rooms it would have closer to 15 floors than 5. You can clearly see 15 2m blocks, so that is 30m, and 8 m down is 38 m total wall height inside. At 3m per floor, with wood floors (thin!), that is a potential 12 'stories' tall. Using very high ceilings and stone floors, though, I think it actually only has like 8.

https://steamcommunity.com/sharedfiles/filedetails/?id=2799499750