A solution that has worked for me is to start with a 4' X 8' sheet of 1/2" plywood, rip it into two pieces of 2' X 8'. It can then be rigged into a table of either 4' X 8' or 2' X 16', according to your needs.
Other touches:
1. I screwed/glued a stiffener onto each piece. Center a 6' long 2"X2" along the bottom.
2. To fasten the table tops together, I use two, 18" chunks of 1" X 2". With the table in a 4'X8" configuration, I drilled through the table top and slats, and bolted the slat across the bottom of the joint. A carriage bolt, flat washer, and a wing nut works nicely here. In the 2'X16' configuration, lay your pre-drilled slats across the top of the joint, and mark where to drill. (This saves having four holes in each slat instead of only two.)
3. At Home Depot/Lowes/Menard's/Wal-Mart/etc. get at least four, metal/plastic saw horses of the same height. I suppose that 5 or 6 horses would be nice, but four seemed to be sufficient for me. This height should be a working height for you - where you have to neither bend over, nor raise your elbows to work. What some call "ergonomic", I just call "geezer comfortable".
4. Enclose this work bench in a 25'X40' pole barn. Said facility should: have a concrete floor, be insulated and both heated and air conditioned, have a stocked wet bar in one corner, have a lounge in the loft, be equipped with copious lighting, and be on the delivery route of a good pizza joint.