Many years ago, I got a hollow core door out of a neighbors trash pile. I checked it for flatness and it was perfect. I took it home and cut it down to four feet. I used it as my building surface up until a couple of years ago. I got a building board from Wright Engineering and I was impressed from the minute I saw it. If there is anything better on the market for a building surface, I can't imagine what it is. Check it out:

Wright Engineering

I know several people who have them and they feel the same as I do about it.

Howard