When I first set up my garage workshop nearly two years ago, I didn't have much time or money to invest, so I just used what resources were available at the time and picked up an old office desk sitting in the backyard. I lined the top with some cardboard and foam to keep it from getting scratched. This simple layout served me well over the years and provided a large surface on which to build projects and assemble engine parts.
To put things lightly, this workbench had the sh*t beat out of it, stained by various chemicals, and more. Eventually, though, the cardboards and foam liners became tattered and torn and required periodic replacement, which became a hassle. Fed up with swapping out the makeshift covers every time I used the table, I upgraded the wood surface by laying an aluminum sheet to create a more durable surface.
A trip to the local metal supply store netted some 5052-grade aluminum (48x144 inches) sheet for the reasonable price of $60. We could have gone with 6061 or stainless, but the prices were more than three times the price of our 5052 aluminum. The fullsize sheet was cut to my desired specs at the store before hauling it back home in my Civic. Keep in mind that aluminum sheets made of 3003 or 5052 thinner gauge thickness are cheaper when purchased in bulk, but softer than steel so it will develop gouges and scuff up easier. Another option is to cover your workbench with galvanized sheetmetal; it is harder than 6061 and has a good shine too.
Will I actually care if there are scratches under all that? Not really. The heaviest thing that we've ever put on the workbench is an aluminum cylinder head. It's good for certain things; it stays clean, doesn't rust, and stays flat. It does, however, make it hard to slide anything heavy on it; magnets don't stick to it and you can't tack anything to it, making it a trade-off.
It's not easy to get nice edges and bends with handtools, but with a little bit of patience, you can get the edges to fold over fairly nice using a rubber or plastic hammer.
We secured the sheet using some 3M double-side adhesive before wiping down the surface with some acetone.