Here's a new fort design that my teammates helped me build on sf_atrium. The basic guideline for how to build it is this.

Here are some photographs of the fort.

As you can see, it has the benefit of being a dynamic, moving flag defense.
More pictures:

Now that you know how to make it I hope to see it used more in pubs because it's really a great design.
If you are so inclined, you can look at the demo of this for in combat which is to giving you a really good look at how good idea it is. I am highly encourage because it shows how a great design this is.
http://files.filefront.com/poohunkde.../fileinfo.html