@MegStringBean97Hi, there
At first, questions to you.
Q1.
you wrote: "I use the build room tool"
Is this mean you use MOD for build?
Q2.
you also wrote: "I have recently updated my Sims 4 and upon building new properties I am unable to create / use second floors."
"unable to use second floors" is in "Live Mode"?
If there is some pics about your issues, we can explain in more details.
If you use MODs, there is something doing able before can't do at getting update. If you do so, at first you do move MODs folder to desktop, and try to play in no MOD.
If you can play no problem, you check the recently MOD status at the website of all MODs you have. And if some update for MOD, update that. After then check your all MODs one by one, or using 50/50 method. About MOD's issue, please you could contact to creator.
How is going on about your issues? Hope already having resolved this.