Advice re: indoor deck/floor

I need some advice on an indoor deck/floor I'm wanting to build inside my metal shed. Shed dimensions are 72x42x18 feet (lxwxh) Floor/ deck surface will be 42 ft by 12 ft. The surface of the deck will be 9 feet above the dirt floor of the metal shed. The building has vertical wooden posts every 7 feet along the walls, and the deck/ flooring will be up against the shed walls on three sides ( both 12 foot sides and a 42 foot side. ). Im planning one set of five foot wide stairs going up.

At first, I thought I'd build it similarly to an outside deck, but then I thought that maybe I could do better given that it won't be exposed to the elements. So I would really appreciate input as to how to best accomplish the following goals:

Goals:

1.) I'm building this for storage

2.) I'd rather overbuild for strength/durability but I have no idea what that actually means in terms of specifics

3.) what are advantages/ disadvantages of building it as a deck vs using plywood as the flooring surface? For instance - would a deck of this size (500sq feet) be cheaper/ stronger using 3/4 inch plywood/osb or would using decking with gaps between the decking be good enough.

I would really appreciate any/all input

Thanks.

Greg