this is what I would build. I just had some water damage and this would have been great as it would be out of the way.
https://www.youtube.com/watch?v=xXZaUoMb-60
That's innovative. However, I would have some concerns. Some of the hardware isn't intended for that type of application; depending on what is used for the layout surface, there could be problems with the platform flexing - cracking the scenery and wreaking havoc with track. Could mitigate the flexing by screwing and gluing plywood to the frame, but would it then be too heavy? Flex would be less of an issue if the frame was rectangular, but it's L-shaped.
Not sure I'd park a car under it.