Man, I just build mine out of 2X4s, made the frame, and then put 3/4 inch Partical board on it. Make the frame straight, the bench will be straight. Then I tape posterboard over it so when I spill glue and stuff, I can just replace the sheets of posterboard and have a new top! Works great. If you like to use pins, then put cellotex over the partical board and tape the posterboard over the top of that.

Makes a great workbench, and cheap too! Specially when you can get the wood from LP factory second store.