I think it looks ok, I just think stone is a depressing material.
I'm a sandstonist and brickist, maybe I should even regret making the hospital out of stone... Hm.
But I think stone is realistic, looking at many concrete skyscrapers (or at least concrete covering the steel frame).
A skyscraper of sandstone doesn't make a lot of sense, a skyscraper of iron would be ridiculously "expensive", and a skyscraper of bricks... Well there are some tall brick buildings...
Stone slabs? Idk. I think it could look okay if you make the walls stone and put some windows. It would probably look weird if one line was stone between each floor, and then some other material. Or the sides could be some different material, with just stone corners.