I'm working on a new Magus for my Cult Mechanicus/Ad Mech/Mechanicum.
After reading more of the Black Library fluff, it's obvious the Mechanicum/Machanicus are some twisted folks. While I didn't want to make my Magos "dark" mechanium, I think there is a lot of opportunity for conversions to make each Ad Mech army unique and I want my general to stand out.
One of my favorite comic book villains is MODOK. A giant head floating on a cyborg body with mental powers and traditional weapons built into his "golden throne." I couldn't figure out how to make a knock-off model out of GW bits, but it did give me a jumping off point by inspiring me to use the dreadnought hull as a body.