I built a steel one. 3/8 thick plate, 36 inches wide 48 inches tall with cut out for a right handed shooter. It has folding legs which is "c" channel 1/4 thick 1.5 leg by 3 inches wide. Very stable, in fact it weighs around 400 lbs. Not to portable as it takes two rather stocky guys to move it. I used headliner spray and glued some outdoor carpet on it.
I now need a trailer to carry it, I've been using my truck but like I said need to guys to mvoe the sucker.
If I were to build another one I think i would use Aluminum as the table top maybe an inch thick and steel legs be a bit more portable but not so heavy.
You can see a partial view of it in this picture Shooting bench