From what you're describing I tend to think I would recommend going through each room and tracing them with regular walls until you complete a room to cover all areas so that all rooms end up with regular walls and floors (which should delete the platforms), then make the walls the height you want them. If this fixes the issue you could then go inside the rooms and add whatever platform areas you want.
Personally, I do not use platforms to make rooms... to avoid these issues. Also, if I use them I keep them one tile away from exterior walls, as sometimes I've seen where having them all the way to the edge of an exterior wall can cause issues. Platforms seem to work best, in my opinion, for special features, not as a primary building tool. For that I would use room/wall tools.
If that doesn't work and you would like to share the home in the gallery and describe what you want done, maybe with some screenshots, I could have a look. Please then share a link to the lot here, or the exact name of it in the gallery.
Or... you are welcome to share some screenshots with more details here of what is happening.
