I built another one last weekend that looks similar to Sullymans picture.
The two differences are:
1) Instead of just using screws to connect the vertical supports to the top & bottom box frames, I drilled two 1/4" holes and used stainless bolts with washers on each side.
You can still start off by screwing to align them if that makes it easier for you to drill.
Bolts were 17 cents each for 1/4" x 5". 4 bolts per leg.
2) I used two 2x4's for each leg and cut one leg 3-1/2" shorter than the other so that one leg is under the top brace (which is a 2x4).
One leg may be enough, but I tend to overbuild and it wasnt much harder to do.
Another advantage to the bolts is that my stands can all be disassembled and put back together. Helped a lot with my recent move, but more importantly I can build in my garage and assemble in the basement.
I agree that the plywood top helps stabilize the stand. Make sure you connect the legs on the bottom in some way, like the box design in Sullymans pic, that is important too.