Sims4 ps4 construction mode / How do I fill the roof gap and set the foundation?

When you build a house, it has this normal flat roof on top. However, this is now missing in a room section and I don't know how I can fill this gap again. I have now built a normal roof on it, but you can still see this gap and unfortunately it bothers.

Then I would still like to build the foundation around my house without my entire rooms being piled up from the inside.

I ask for help. 🤯

A picture would help.

I CAN'T Help YOU WITH THE FOUNDATION SORRY):

BUT the gap in the room does not go away in my opinion the problem I had before and it was said (by friends) that it does not work and as far as I know it does not work either

hope i could help with that