@Pick-a-boo_doo You ask some very good questions, and make some excellent points!
In the case of the ceiling disappearing over the platform, in my examples above the roof did not disappear - neither when the platform was not touching a wall nor when the platform did touch a wall. However, when I added the platform in the middle of the room the other day (for that other bug report test), the ceiling did disappear! So... I'm glad you asked about this.
I just went in and tested further in that room I mentioned testing on for the bug report. I found that if I made the platform in middle of the room, the ceiling did not disappear. However, if I made the platform outside the room (in this case on the ground), then used the move tool to place the platform inside the room, then the ceiling did disappear.
Edit: I tested further on the disappearing ceiling and found that the method of producing the disappearing ceiling mentioned above did not work when I moved the platform from the yard to inside a room in the main house on the lot - which has a raised foundation. It only happened when It moved the platform from the yard with the move tool to a different building on the lot that has one level only and does not have a raised foundation. So... if that detail is of any help, there it is.
Thank you for bringing that up, and I will add that information to the bug report for clarification! 🙌
And yes, using the 'build ceiling' method does work with the missing platform ceiling (this is my favorite way to do it). However, I wanted to note that highlighting the platform then looking top-down didn't bring up the yellow 'build ceiling' border for me... however it did work via the way I normally do... highlight the platform (by selecting it) then go up a level (with the platform still highlighted) to get the yellow 'build ceiling' rim option.