ᐅ Flooring for the Tool Shed – OSB Panels or Floorboards?

I am about to build my wooden garden shed, which will stand on a profiled timber frame supported by screw foundations.

Now I am considering how to construct the floor. The manufacturer usually offers untreated 19mm (3/4 inch) boards for this, but these are currently unavailable, so that option is off the table.

As an alternative, I have looked into using OSB panels, but I am unsure about moisture issues since the shed has a cavity underneath. Despite possible impregnation, mold could still develop.

However, I could also consider using basic pressure-treated decking boards as the subfloor. These already provide some protection, are made from the same wood as the frame, and would allow me to add cross battens to the profiled timber frame.

Has anyone had experience with this? Or are there other alternatives?

There are special OSB boards of class 3 or 4 that are (conditionally) suitable for outdoor use. Additionally, there are waterproof glued plywood sheets, which are also used, for example, in trailers. Bauhaus offers quite affordable options. However, cut edges must be sealed without fail.

I would use pressure-impregnated planed tongue-and-groove boards. Affordable, easy to work with, and provides a neat, smooth floor.