I want to build the top of my work bench out of 2x12s. Part of the bench will be 12" wide, part will be 24" wide and part will be 36" wide approx. What is the best way to frame it to a flat wall of OSB board? Also I want to put shelves under it with doors. I have 20' of wall to use up. Left to right will be 5' of 24", then 4' of 12", then 7' of 24", 4' of 36". No doors on the 12" and the 36". Maybe simple work bench was the wrong site to start looking, but it would be simple if I had paid attention in shop class! Thank you for your time.