I'd be interested. I haven't done much with the system (mostly just making characters for a DH game that never got anywhere on these boards). I know the game and the lore/fluff, but I don't know as much regarding the specifics of the rules off the top of my head. I'd have to find that stuff online.
Most likely I'd go for a Librarian, I think, or maybe try and throw a specific concept (which I remember that Deathwatch didn't quite work with at first).
Any chance of a Grey Knight, if I call dibs? :) If not, very likely Dark Angel.