I have 2 solid core doors side by side (so the bench is 80 x 72 inches), with 2x4 framing to hold the perimeter together underneath. Then I used some sort of generic shop (drawer) cabinets at the corners to hold it up at about 42 inches working height. The whole thing is screwed together with big wood screws so you can take it apart. I used to have a glass plate over 1/2 of it, to help make sure it is flat. Getting the thing flat is the tricky part.
make sure you get a height you like, this make a huge difference.