That looks nicer than my dinner table!!
I have a fully braced sheet of 18mm ply (longitudinal bracings at 10" centres and a few cross braces as well)
This sits on some beefy sawhorses, made from 2x4s. In fact, they are seriously beefy
, and stackable. I got the plans
here
The working height might be a bit tall for some, but I'm 6ft3, and once the chassis is fully welded, it will just sit on the saw horses, thus lowering it by nearly 4", ready for the rest of the work
The curvature in this pic is from the camera lens (crappy little compact digicam)
As you can see, I also slung a few spare 3x2s underneath, between the sawhorses. These are for storage.
The bracing is inset from the edge of the table to give room for clamping. I also drilled 30mm Dia holes around the edge (3No. on the long sides and 1No. on each short side), this is to enable me to just drop the end of my welding torch through, it then sits there perfectly.
Another little tip - don't clamp stuff to the egde of the bench for plasma cutting
it starts to smoke a bit