I apologize if I'm not making sense, as I may be misunderstanding the question. If so, please not sure if this is what you mean, but if you put a roof on the first floor and you want to go up a level (roof up) and add a second floor but not have it delete the roof you have on the first floor, then yes and no.

I have occasionally literally moved a roof up a level (or just sat it on the ground temporarily) before in order to add it back onto another floor level or to put back in place after making a room. At least at first, part of your struggle will be setting up your own household and this can, if you want, be quite literal. It’s an extremely open-ended title, and in most cases, you need to invent your own goals. It all depends on how you make the second floor and what type of roofing you had already added to the first floor. Every game in The Sims franchise has emphasized open-ended gameplay, and The Sims 4 is no exception. Sometimes making the rooms on the second floor will simply delete the roof, and sometimes the roof that was there may not 'clip' where it meets the new room and may go right into it (not the normal behavior, but sometimes it happens). The Sims 4 allow you to build up to 4 levels above ground and 2 levels under ground. If you have a roof on the first floor, and you go to the second floor and begin creating rooms on that level, you will usually see the roof that you made already 'clip' (disappear) in the areas where you make the new rooms there. This means houses like basement + 3 floors + roof or terrace.

not sure if this is what you mean, but if you put a roof on the first floor and you want to go up a level (roof up) and add a second floor but not have it delete the roof you have on the first floor, then yes and no.

Sims 4 add second floor