Value of private rooftop deck?

[Mitchell J.]

Curious to see what everyone thinks here.  How would you value a private rooftop deck that comes with a top-floor condo unit (of a 3-4 unit property)?  I know they come in different shapes and sizes, but how much of a premium (as a % of the total value of the house, or $ amount) would you say a finished private rooftop deck with a Chicago skyline view adds?