Textanker,

I concur with Lee, use solid core doors. I have two of them in my shop and you will not find a better, smoother, more solid work surface than these. I also used 4x4's for legs. It is heavy, but is well worth it. You can also mount one against a wall for "general" workbench use by only using 2 - 4x4's. Just screw a 2x4 into the wall studs, horizontally and level, at the desired height. Measure from the floor to the top of the 2x4 and cut two 4x4's to that length. Attach the 2 - 4x4's on two corners (or inset if you like) of one long edge of the door. The other edge will rest on top of the 2x4 and against the wall. Now just put a few screws from the top along that wall edge (3 should do.. one each corner and one in the middle) these are not load bearing.. they just keep the bench in place) and there ya go. Although it's nearly a must to have one free-standing table out in the middle of your shop for building planes, it's also nice to have a solid bench on one wall. I have a vice mounted on one end and a bench grinder on the other. Also you should seriously think about mounting a peg board in your shop, and there is no better place than on the wall above the aforementioned work bench. They are cheap and easy to install. You can get all kinds of hangers and hang all kinds of stuff from them. I also mounted many magnetic tools trips on them to hold a lot of little tools (great for screwdrivers and ignition wrenches, or anything that is metal and does not have a hole in it) If you get really bored, you can also put an air compressor in your shop and route the air to different places around the shop with PVC as I did, you would not believe how much you would use it if you had one.... but that's another story, and I use my shop for more than building planes.

Good Luck,
Monty