Sorry, but I don't see this as such a great deal. You apparently have nothing to bring to the table besides an idea, and you expect a programmer to devote their time and expertise to develop the business, in return for a vague promise of profits. And all that programming effort to develop your product is worth 50%, where just the idea is worth 50%?
How do you intend to monetize it? Who determines when this "takes off"? What happens during all those years until it makes any money? Who pays the ongoing costs? And, I guess the programmer continues to work for free maintaining and updating the site until it "takes off"?
And, frankly, I don't believe you've thought through the technical aspects of this idea of yours.