Anybody ever seen any in any book?

I'm trying to figure out how they'd differ from normal constructs.

I'm thinking crits and sneak attacks would be possible, as they have important parts and cogs to damage, unlike a golem. However, players wouldn't necessarily know where those are, so perhaps give them fortification as an armor quality?

Like any construct, I'm thinking no con score and a d10 hit die...but i'm not sure. (i'm trying to build a clockwork dragon, and the 2d12 hit die will be missed.)