Games Workshop has just posted the thirteenth mission for Space Hulk. Click here to download the PDF. Mission XIII is not really a mission, but rather a series of steps to help you design your own missions. The PDF is a template to record your mission rules, objectives, etc. as well as to record your map on a grid.
While not what I expected, it's still a decent guideline for creating your own. Man, the ideas are already coming to me. But the only thing that stinks about the article by GW is that, they only placed the template in downloadable PDF form. I would have loved a downloadable version of the article in it's entirity.