I saw the "John Bridge Making Program" post, and since my computercraft skills are a little rusty, I thought I'd try to make my own bridge program.

This will attempt to build a bridge of whatever length you have decided, and will automatically adjust its height to go over obstacles. Unfortunately, this requires two passes. Another problem is when it goes underneath an obstacle, it is able to back out and go up until it goes over the obstacle, but then the length is not correct.

http://pastebin.com/UV14jR2Y