I raised a the roof on a two storey farmhouse by shuttering all round and filling with concrete. The stone wouldn't have been stable enough to put block on it. I added an extra 2 feet on.
It would be rare enough for a single storey stone wall and its foundations to be specified and built to the stadards required to support a two storey structure. A stone wall like that may not even have foundations, so you could potentially require underpinning to build on top of this.
You'll definitely need an engineer to assess it. I'm no expert, but my gut tells me what you want to do will not be possible without somehow reinforcing the existing wall & foundations. A good engineer will tell you if it even makes sense to go with a cavity wall on top of stone.