There are so many flat roofs everywhere, that aren't in use as roof-terraces. Whether it's because of regulations, or because of the costs attached to it, or whatever reason one could think of, many flat roofs just lie there without being in use for anything else than sheltering the people living under it.
There must be other ways, is what the architects of Kalhöfer-Korschildgen must have thought. So they came up with a mobile roof terrace. It is a bit like those mobile picnic tables that you can fold into a suitcase an carry with you. I this case, you can fold out a roof terrace from the inside out.
If the weather is right, you can open up the skylight in your house and unfold the roof terrace package out of it, and everything is there: chairs, table, tablecloth, plates, glasses and cutlery. A brilliant solution for roofs without permanent terraces.