There actually was an Airstream motor home that had that exact feature. It was called the Sky Deck if memory serves me correctly. Ironically there was one in Gaffney when we were there at Freightliner a few weeks ago. I didn't get a chance to chat with the owner as I would have loved to see how it worked. I remember seeing write ups on that particular model and it used a lot of floor space up with the stairs going up to the roof.
2011 Berkshire 390bh