Back in the day at a Games Day someone had scratch built (out of cardboard) a Grey Knight Titan.
This was an impressive model and I really liked it.
I have for many (many) years being attempting to build a force of Inquisitorial forces and Grey Knights, but purposefully trying to to create Grey Knight versions of standard Space Marines, both infantry and vehicles.
I do like the concept of the Imperial Knights and looking over the range of models I did think that the Armiger Warglaive could be the basis of a Grey Knight version, complete with protective purity seals, additonal sheilds, even a new head, etc…
I really do need to though paint stuff, rather than buy stuff, so for the moment I am (just) thinking about this project, rather than doing anything concrete about it. However watch this space!