I've been working on this for a while and thought I'd finally share it with people. Here's some blurb:
"This book details the history and organisation of the Storm Hawks Space Marine chapter, a chapter of unknown origin with close links to the Mechanicum of Mars. You will also find rules for Special Characters and their personal background, as well as specialist units only available to the Storm Hawks chapter."
And here's where you can download it from:
I've posted the Codex on the Codex Project forums, so fingers crossed it gets certified!