The standard shed floor is ⅝ inch CDX Plywood
You can upgrade to ¾ inch CDX or Treated.
Treated Plywood is excellent for harsh environments where it will be wet for extended periods, the ¾ inch CDX Plywood allows for heavier loads over the standard ⅝ inch.
In most cases the ⅝ inch flooring is very suitable, upgrade is recommended if you will be storing very heavy items such as Motorcycle, ATV, Riding Mower, etc.,
*We do not use OSB on floors! OSB is not a preferred product for floors.