Needless to say, it varies WILDLY depending on the style of construction and if it's commercial (Offices) or residential (apartments). Early 20th century skyscrapers tend to be massive commercial structures. Those going up now tend to be "super-slim" residential structures featuring whole-floor condos.

I don't know what the payback on a early 20th century style building would be today. But a modern "super-slim" like One57 or 220 Central Park South would cost about $1.6 billion, take roughly five years to build, and would recoup its expenses between two to three years after construction finishes since they are selling and not renting those condos.

So, if you're talking about the sort of skyscraper being built now in New York then roughly 7-8 years.