This is the set up I designed and use. Doesn't look like much, but I can store 12 garden tractors in roughly a 12' x 12' area. It tractor weigh in right around 600 pounds each.
The platform consists of 6 elevated shelves, supported by 4" x 4" posts. The post set in 6" PVC piping that was cemented into the ground. I first dug my holes about 12" diameter, poured a good 4" think footer at the base, center my 6" PVC pipe, then poured roughly 3" of concrete around the perimeter of the PVC, keeping the center of the pipe hollow. Once the concrete was set up, I chamfered the corners of the 4" x 4" post so that it would fit down inside the PVC pipe and set firmly on the concrete footer. After determining the height needed for clearing the steering wheels and lift handles, I cut the posts to the heights required. I laid my posts out in this type of layout ( : : : )
Each elevated tractor sets on it own shelf platform, roughly 3' wide by 6' long. The framing for each of the platforms is out of 2 x 6's, spaced on 16" centers, and I used 3/4" plywood for the decking. The framing that supports each shelf are 2 x 12's. These are not nailed to the 4" x 4" posts, so that they can be removable. I nailed 6" long 2 x 4 blocks to the posts, roughly 11 1/2" down from the top of my support posts, as these will be what supports the 2 x 12's. To the face of these 6" 2 x 4's, I nailed 17 1/2" long 2 x 4's, keeping the bottom of both 2 x 4's even. This will keep the 2 x 12's from rolling or falling over while sitting on top of the 6" 2 x 4's.
If you look at the picture, you can kind of tell what I'm trying to explain above. This system works really well, and the nice part about it is, it is all removable. I can remove just one shelf, or all of the front three shelves, or one front and one back shelf. The posts all lift out of their holes, so the only thing that isn't removable are the 6" PVC pipes cemented into the ground, or in you case, the floor. One thing that I would recommend with this shelving system, is that you should try and utilize at least two good walls to help give the whole set up stability. In the picture, I framed the shelving system between three walls of a pole shed that I had at my old residence. At our current residence, I only use two walls. No changes in the effect, and the system still works great. I just don't recommend trying this system as a free standing structure.
As for getting my tractors up or down off of the shelf, I built what I call as a half shelf. Basically it is a framed box made out of 4" x 4" posts and 2 x 6's, with a finished height that equals half the height of my elevated shelves and the finished floor. I simply ramp my tractor up onto the half shelf, then ramp it again up onto the shelf. For my heavier tractors, I used a winch and straps to help pull the tractor up.
Might not be what you are looking for, but I thought I'd just throw it out there for you as an alternative method to think about. Good luck to you with what ever you decide to do.
Edited by johndeereelfman, December 02, 2013 - 07:59 PM.