I will add to Mechans' very solid advice that you can use eastern rock maple boards as shelves http://www.boosblock.com/categories_for?cat_id=4802
My rack(s) use these, and on one I have an additional, very heavy 3" thick maple platform supporting a 300 lb turntable
My rack(s) use these, and on one I have an additional, very heavy 3" thick maple platform supporting a 300 lb turntable