I have this problem as well ☹️
I can confirm it's not something dirty on the roof, i actually destroyed and rebuilt the entire terrace in an attempt to fix it and the problem came right back.
Check your inventory.
A good tip to get something dirty in an inaccessible place is to hire a scheduled maid Travel to somewhere else before her work schedule starts and return later. you will get a note that a maid cleaned the house and everything dirty has been removed by the game.
It literally only happens on the roof terrace, my sim is fine everywhere else, but when I do "check dust levels" on the roof it says it's dirty.
It's nothing in the inventory, and I'm not gonna hire a maid every week just because of a bug :/
That floors get dusty when you have bust the dust kit installed is not a bug. That is supposed to happen. You can Vacuum yourself or buy a robot vacuum and fully upgrade it. One on each floor with a schedule set for every 6 hours will keep the dust away. Since it is outdoors you will need a neat sim or a robovac to do the vacuuming.
This "is" a dust problem. I have a flat roof. Placed a ladder on the outside of the house for access. I also have wind turbines and solar panels up there, not the roof kind, but the ground ones that you have to fix from time to time. So access to the roof was necessary. The noodles comes up everytime my Sims are up there. When I check the dust level on the roof, it says "it's filthy." The option to deep vacuum comes up, but the action is never performed. It fails. There is no "I can't do this" animation or something indicating a routing problem. It's just canceled. Vacuuming inside the house works as normal. And no, there are no dishes or anything else on the roof. The solar panels would be the only possibility and they have all been cleaned, and are cleaned when they get dirty.
