A floating deck is typically, as I understand it, not "lumber on the ground". It is lumber on "Dek Blocks" or similar, with posts as needed (which could be anywhere from nothing (on the highest natural spots) to several inches to a few feet tall) sitting in the Dek Blocks to support the deck frame in a level manner.
A floating deck is definitely a DIY project. It is quite different from a traditional deck: No footings to pour, no critical connection to the house, often no permits required. Permits are almost always required for a traditional deck. For a floating deck, the rules vary by jurisdiction - e.g., in my area (at least when I built my floating deck), no permit required up to 200 square feet.
As far as snow & rain, there are two issues - top and bottom. For the top, make sure that there is enough of a gap between the decking boards for water/melting snow to drain. For the bottom, if the boards are pressure treated and on top of blocks, you should be fine, as the rain and melting snow won't collect underneath. But if you put the frame directly on the patio then you could easily have sections where water would collect and cause problems, even with pressure treated wood.