The plywood part is easy. I painted the underneath white and the sides with the same Rustoleum Painters Touch from Home Depot, I've mention before. (Its really smooth). Then I stained the raw wood 2 times and then sanded it to really smooth out the the color and the surface. (if you didn't know stain, pulls up the wood as it stains giving it a rough feel.) Then, polyurethane! I did 5 coats of a satin finish to really get a smooth cleanable workspace! 

I like this DIY  because, this allows the average 29" chair to fit underneath. Other DIY's add a 1x4 across and you'll have a hard time finding a chair to fit! The chair I got from Good Will and it was sturdy so I just replaced the fabric!
The chair cost $11 and the fabric I had in my collection. tip: Choose a thicker fabric to avoid "fuzziness" or holes if you use the chair a lot. When I took off the old stained fabric, the foam had no problems so I decided to reuse it to save some money. When you remove the seat with a screw driver, you'll see all the staples you'll have to remove and this can be a process. If you don't have a professional staple remover, then just use a thin flat head and some pliers. You'll definitely need a staple gun. The one above, I got from Home Depot for $30 dollars, but I use it a lot in the house, so if your husband/boyfriend/partner doesn't have one, I can say its worth the investment. Make sure you pull the fabric tight with the foam in place. If your not coordinated very well, you'll need a little help. Cut off any excess fabric, so it doesn't hang down when you screw the chair back in. Or you can get staple an inexpensive fabric on the bottom for more aesthetic purposes. tip: Also, make sure you are conscience of all the screw holes, so you don't staple over them. And done! Not bad for an $11 chair...