If I understand Wikipedia’s article on tree lines[0] correctly, the variant usually referred to is due to coldness and snowpack[1]. I have trouble imagining considerable snowpack on a building that would not also occur on the ground and cities (where you would most likely find skyscrapers) tend to be a little warmer than the surrounding countryside anyways.

[0] https://en.wikipedia.org/wiki/Tree_line [1] Alpine, ibid.