one of the tables at work is made of a 6x12 piece of 1" plate on an ibeam frame, some of the other tables we have are topped with 3/8" plate, but its hard to get those leveled out so they dont have high spots..... def build a good level frame with adjustable legs every 3-4ft, so your plate will stay flat, i'd recommend 3/8" minimum, but unless the table is really small, you are gonna spend some $$$....