The photo above shows the pieces for the first board mocked up for size. The biggest problem is the size of sheet material here. If it has been cut in the USA then it will be in feet but if it's been made here it will be metric and thus a little short in every direction. Construction will be pine as it's pretty cheap running at $0.97 AUD a metre here.
Thinking music here...
I decided to go with 3mm MDF which has come from the US and has been cut into 4' x 2' sheets. I'd prefer ply for its extra strength but aren't prepared to wear the waste of cutting down a big sheet. Not to mention cutting the sheets by hand.
Board one screwed together. I toyed with the idea of using a long board down the middle but this double brace going across should be stronger and uses up scrap from around the place.
And an example of how it will work on a trestle table. With another one or two bolted to it shouldn't move too much. I've now nailed and glued the top on and that's sitting in the shed with some weights on top.