There's a plan onj my site for a bench.. www.aerotech.com, and click 'plans'

We used 1" MDF and seems to be flat, and tough. We then through on a sheet of Gyprock / wall board. Works for us..

Tyheh door is treh next best thing, and placed on top of a cabinet, great idea!

Sometimes a dining room table, at teh local 2nd hand store is ideal, just bring alon a straightedge to check it before buying.