The shed is a lifted a few inches and over gravel. It currently has plywood flooring. It is a very nice shed so I thought it would be a good idea to invest in a durable flooring to protect against wear and tear (push lawn mower, liquid spills, muddy boots).
Look at a flooring store for sheet vinyl also called linoleum, remnants (the end of rolls). They can be inexpensive and would be seamless. An alternative that would be more slip resistant is something we call locally porchpaint. It covers many New england porches. It is only available in gray and is an oil based enamal. You can spread sand on it while wet to increase traction. I have had it last 10 years on a porch floor.
If it's only a couple inches above the gravel, you might consider ripping out the floor and redoing it interlocking brick or patio pavers.