My camera batteries are dead, so I'll have to post a pic later. I built mine in place, attached to the floor. I had to do it this way because my basement floor isn't exactly level or smooth. Anyway, I built a fame out of 2x6 lumber, basically like you would build a floor, with joists on 14" centers. I covered it with 2 lays of 3/4" plywood. The second layer was purely to add extra height. I also used plywood around the outside edges. I used a layer of cork on top for some sound/vibration damping. When I eventually tile the floor, I'll place tile up the sides of the platform as well.

Think of a box with 2x4s or 2x6s at each corner. Putting in a drawer would be optional, but not a bad idea. you could also paint it to match the units (white) or anything else that suits your fancy.

Also remember that the washer and dryer are supported at the corners (where the feet are), not the middle so that's where the strength should be.