I'm building a walnut veneered "countertop" for a built-in office credenza, 11 feet long, 21" deep. I've found a source for 12 foot long veneer, so no problem there. The question is the substrate. For a plastic laminate countertop, I'd use 3/4" MDF (two lengths with a couple of joint connectors), and feel comfortable that I could maneuver the assembly from the shop to the office without it coming apart. I'm leery about doing it with veneer and have thought about overlapping 1/2" MDF sheets to make up a 1" top (there will be a solid edge-band). Other questions: Do I need to worry about warping and veneer the underside if it's screwed in well from below (think kitchen countertop), and what's the best veneer glue (no vacuum bag available)? Thanks!