If you're doing it for your own enjoyment, go for it! We shouldn't just bed down in our houses at the end of the night but genuinely enjoy their amenities while we live there. Will it pay off for you seems to be your question.
The best return of any remodel is kitchen and bathrooms. Period. What your deck may do though is not improve it's VALUE but rather improve its SALEABILITY at the end. Two homes near each other and all things being mostly equal if they sell for the same price and one has a roof deck and another doesn't, most people would chose the one with the roof deck. They may never use it, but people buying homes will think, "oh, we will have the coolest parties out here!"
Important note, if you're getting it done, get quality work done with all the appropriate permits and don't skimp. If someone sees a roof deck on a home they are thinking of buying and it looks like the roof deck is going to fall right through the roof, or it's faded or warped, or it's such a monstrosity rather then being a beautiful simple deck that fits with the surrounding neighborhood, you may cost yourself a sale.
I'm not in your area but I have professional associates in the area. If you would like a recommendation to one to perform a free market evaluation of your home before you get started, just drop me an email or give me a call.
Technology Committee Chairperson