This spring we had a "semi-prebuilt" tractor shed installed by a local firm employing Amish workers. They brought in pre-built sections on a trailer and built the entire 12x20 structure in about 3 hours (while still doing very high quality work). We told the local firm that we'd be putting ~5K lb. tractor in the shed, and they recommended doing tongue and groove boards to handle the weight. I'll have to look up the dimensions of the boards that were used, but there is no question that the floor is stout.
The ground prep subcontractor did a good job leveling off the site and putting down >6" of gravel to support the shed bottom wood. I preferred this approach because it gets the floor boards off the ground so they cannot sit in water, and there's good drainage through the gravel to the adjacent down-sloping land to minimize the potential for the foundation wood to rot.
The ground prep subcontractor did a good job leveling off the site and putting down >6" of gravel to support the shed bottom wood. I preferred this approach because it gets the floor boards off the ground so they cannot sit in water, and there's good drainage through the gravel to the adjacent down-sloping land to minimize the potential for the foundation wood to rot.