I am a little confused why are you putting a heavy timber floor over a concrete base would it not be better to use the base which is plenty strong if it was a garage you could have a finished floor of glued up chipboard layed on poly. to make it smooth. If the building sits on the edge of the base just bolt it down (dpc and treated for wall plate ) and the cladding overlaps the base there are no problems with water getting to the structure. click my www button and look through the construction pics for extra info/ideas.