I have the entire 48x88 pad level now with cement blocks (level on sloped yard). I have one corner that needs about 1/2" and one that needs 1.5" of lift. Should I just shim with shingles or cut down some wood and shim with that? If it gets wet it would rot....and I don't want it to rot out...cause once this thing is built it will weigh a ton and I won't be able to really move it. Suggestions/advice? Thanks!