Have you looked at this? https://youtu.be/TbvAJmf9Lg4
I haven't tried to make a room myself yet but this video has helped my friends.

Yes i know about the problems with corners but this isint that, but thanks. In debug i have full wall enclosure. The rooms show they are not fully roofed. the rooms are not roofed because there's no ceiling/floor between the two levels because i want balconies/ tall ceilings.

Did you ever find a solution to this? I had this exact problem about 2 years ago when the popular building mod was More Builds. It added a 99% transparent "gym mat" floor tile which I used to make two story tall ceilings exactly as you described. However I've just started a new playthrough with friends, and More Builds has since been made obsolete. I've been digging around to find an alternative solution which is how I found this thread.

For anyone who finds this in future or doesn't understand what we're talking about:
Player made structures have really iffy room detection, and part of the room detection requires a roof to count as "indoors." This roof MUST be one floor above in order for it to count. If you build a two story tall room and put a roof over the second story (like OPs example), the structure won't count as a room because "high ceiling" two-floor rooms are not supported for player buildings.
Using an invisible tile to make a "roof" on the first floor can fake the visual effect of high ceilings while also ensuring it counts as indoors.

引用自 Lou：

Anyone have any mod/cheat solution to make an invisible tile or mark a tile as floor/roof to complete a room? i have a couple rooms built that take up 2 floors but because there isint a full floor between the two rooms its considerd outside.

---roof--
| |
| | no floor
| |
---Floor-

I need to find maybe a transparent tile or whatever the devs do in there prebuilts. I have glass roofs from buildmenu but i want 100% transparency.

Did you find a solution friend? Came about this and I m really looking for an answer