I am building a wall to make two rooms out of my former garage. The floor is concrete. I will be putting down a 6 mm vapor barrier on the floor. Do I need to put that barrier under the pt wood that I will use as my base plate for my wall of which I plan on anchoring to the floor? I also have approximately 1/4 to 3/4 of an inch difference in the level of the concrete over the 20' span where the wall will go? Can this be shimmed and is there such a thing as pt shims? Thanks for advice in advance!