Raising the roof and adding an additional floor is basically possible. I haven't seen it firsthand yet, but where we always go on vacation, someone has tried it. During the process, the roof structure was damaged... The problem is that it can't be done with just a bit of masonry. You still need space for a staircase, a new thermal envelope, plastering has to be done, and then the expansion of the rooms upstairs. The upper part would probably be painted with a different color, otherwise the transition would always remain visible.