I am building a deck on a concrete patio. The patio already does have a roof. It won’t get too wet during a rain and we don’t get much rain during the summer (Northern California).

I plan to do the framing with 2x4s, which will sit on the concrete.

* What should I use to best break the contact between the framing and the concrete to not trap moisture? Shims or tape flashing?
* Should I use brown colored ground contact 2x4‘s or should regular ones be fine? (Slab is raised and about 8 inches above the soil)