You mean the tent in a box idea? They have been around since the 60s and there are a few aftermarket companies (Hannibal, maggiolina) make them.
I worked in the roof rack industry for years and came across these products a few times. don't get me wrong, I think they are really cool, but what has always puzzled me about them is they seem to forget about the maximum permissible roof load of the vehicle is usually 75kg-100kg.
Now I know that is set as a dynamic (ie moving) load and technically a static load could possibly be higher, manufacturers only state the one max figure.