for the top I use 2 layers of MDF and then a single sheet of hardboard. wrap the top with 1 by material which keeps the hardboard from moving around since you don't want to attach it. When becomes beat up just replace the hardboard. I also used 4x4's for the legs with 1 by material let into the 4x4 legs. I can use a sledge hammer on my work benches without telltale damage once the hardboard is replaced. Note: that I do not do this myself but that is how sturdy they are.
