A bit big maybe...

[MarcoSkoll]

Hmm.

Having thought about it, I might be tempted to underscale an Inquisitor scale Titan a bit. Even if you took a couple of inches off their height, they'd still be vast - and easily more than big enough to illustrate the sheer size of these things. But they wouldn't be quite so impractically huge.

I think the fact that such a model would be a significant proportion of the size of the players would quite make up for the fact it wasn't quite big enough compared to the models.

Monodominant has commandeered this Reaver to shell a city to dust for a minor infraction, and another Inquisitor decides this is unacceptable...

And what exactly is this Inquisitor going to do to stop a Titan? To quote Silva* on the subject of a large gribbly beast:
"Well, you could wave your silver jewellery in its face and order it to stop in the name of the Emperor - or, I could tell it that it's an awful rampaging monster and its mother would be ashamed. At that point, I'm hoping it'll commit suicide."

*In which, I suppose that I'm strictly quoting myself. But saying that would be dishonest - she said it, not me.

[Molotov]

I can imagine constructing parts of a titan to play a game of Inquisitor - fighting inside a titan, or on top of one of the larger ones (an Emperor or somesuch) could be interesting. I can imagine a team of Inquisitorial operatives inserting onto a titan via Grav-Chute and fighting their way to an access door...

[DapperAnarchist]

While Inquisitor Monodominant-Loveskilling is alive, Princeps Wouldliketoseetomorrow won't accept new orders. Kill or capture him, and the Princeps will accept your Inquisitorial authority.

[Alyster Wick]

My first Inquisitor game featured a gigantic AT-AT toy (http://lh3.ggpht.com/_eRswV8Of8IE/Sa7UmsKWmoI/AAAAAAAACKw/dOsCWQpVPYU/AT%20AT%20Walker%20005_thumb.jpg) as a non-canonical titan.  The game took place in a hangar bay.  Some mad techpriest decided to construct this bay on a circular platform suspended in the middle of nowhere with a floor the consistency of a patterned green tablecloth...

Plot holes and lack of resources/story aside, I will say that an inactive titan makes for a fun and decorative centerpiece. If designed correctly you could have a massive Titan who only needs to appear from the shoulders up with anything below that point being painted black to symbolize a character falling to their doom.  I know it could be problematic in that characters could die incredibly easily, but just picture two inquisitors, the radical and the puritan, daemon blade versus powersword, doing battle on the shoulder blade of a titan. You know you want to...

[Inquisitor Cade]

If you were going to convert that thing into a Reaver you'd might as well not use it for a base. A better idea, I think, would be to make it a civilian work platform, a mining rig or what have you. The cockpit could be converted to a bridge where multiple characters could interact, a few ladders and doors, and you've got a one piece terrain.