Have you ever worked with slotted metal before? They cut with a hack saw, but once assembled with screws they're ready to take on the world. Think of these tables as an erector set of sorts, but with less pieces and easier instructions!
You could use any wood you wish for the top, but in this case a simple sheet of plywood will do. It's been sealed to keep out moisture and give things that urban chic look while sticking to a budget. It's a great project that doesn't even involve a hammer! Check out all the details on making your own over at Lowe's.