Not much prior DIY experience here but wanted to build my own shed on top of concrete. However, because of heavy rains, concrete could get wet inside shed and I keep some boxes there that may get wet. (Melbourne weather)
I'm looking for a structure that I could put underneath the shed over the concrete and checked Decko tiles (or any deck tiles). The tiles has a height of 20mm, is 20mm height clearance enough for the boxes I have inside the shed not to get wet? Is it too low? Any alternatives for this?
Image below is what I was thinking of doing where the grey colour around is concrete. Any advice? thanks!

