Is the deck over living space or cantilevered out on joists? What are the proposed joist sizes? What kind of slope is designed into the framing? Finally, never design or build a deck that is level with or higher than the interior floor. This applies to any deck, but it's essential for a waterproof deck over living space.
Thankfully some very talented people have spent a lot of time working out all the details of making a wood deck waterproof. They all are based on physically catching water under the deck with panels that act like a big eaves trough.
DEK Drain even offers systems that allow for the installation of a finished under deck ceiling, complete with lights and a fan, making for the ultimate outdoor escape. Or, it can simply provide a secure under deck storage area for lawn care equipment, bicycles, and oversized toys that have been cluttering your garage. However, the benefits of waterproofing the space under your deck go beyond adding outdoor living space or storage space.