A concrete shed floor is your only real option for such uses and clearly it will withstand the rigours of parking up tractors and other farm machinery that you may wish to store in your shed.
Concrete Shed Floor
Building a concrete shed floor is necessary if you do require long term use and functionality of your shed and it is really a good investment even thought there is a little extra investment involved.
Your starting point will be the use of an excavating machine to ensure that you have a good, level firm base into which you will place your hard core. Once this is done you need to level it with a vibrating machine which will ensure a nice smooth surface.
Do take care to use a sheet of damp proof membrane or plastic to ensure that you don't suffer from rising damp in months or years to come.
Wooden Shed Floor
A wooden shed floor is more than adequate if your storage shed is merely to store small garden implements such as lawn mowers, rakes, shovels, spades etc and in this circumstance you can make your wooden shed floor after you have erected your shed.
Generally you will need plywood for your floor, at least 3/4 inch or fir planking and it is a relatively straightforward task to put in your floor. Essentially you will need to measure up well and hopefully your shed is square to begin with; you need to place 4 framing members around the inside of your shed and ensure that you end up with a floor which is raised off the ground and level.
Start with the highest point with your framing members and nail the plywood to them ensuring that you have a smooth, level surface.