storage building wood deck build

[Tmag]

3/4 plywood will be fine for the floor. Just be sure any and all water will run past the floor and not on it. It is do-able.

[Cooper]

Use 2"x 6" treated lumber for all of the structure.(including the decking)
Put the sub floor framing on 16" centers and add additional blocks/pads under the sub floor or cross members and you want have any problems.
This will add support and keep the floor straight and even.

Also, treat the structure with Thompson Water Seal before you install the building.
You want have to worry about it for several years.
That's my 2 cents worth.

[WCB]

I have a 10'X10' shed sitting on a 11'X12' 3/4" treated plywood floor on top of 4X4 treated post on top of cinder blocks. Been that way for 5 or so years and still is in fine shape.
That floor will be there long after a tornado or nuclear explosion...

[Mudslinger]

If you do decide to treat the deck before you build the building on top, don't use Thompson's, it has to be the worst on the market. A lot better wood treatment like Penofin, Cabot's, Wood Defender to use.