Developers are smart and know real estate. Sure, you could offer it to him, but he's gonna want it at the cheapest price he can get. If you list it with a Realtor, the Realtor will offer it to the developer and everybody else out there in the market looking for a home. You can get the developer arguing with another buyer, and they will be arguing the price UP!
So, find a Realtor you can trust that will do a great job of marketing, particularly on the internet, and price it aggressively to get multiple offers.
And I'd love for you to check out my marketing package, Extreme Marketing. I love showing off great homes.