So each would have its own collection here are some ideas and references if this moves along.
Just a tidbit of information but all these creatures have appeared in Ray Harryhausen movies. Which growing up as a kid I watched quite often.
Bronze Colossus:(I have an image of a silent and still colossus sitting on a throne surrounded by statues he has placed around himself as some sort of bizarre trap or maybe a cure for loneliness.)
(In "Jason and the Argonauts" the Bronze Colossus was trying to recover a needle stolen from a God's Jewelry Box)
-Statues
Dragons:Quotes from wiki
Dragons are covetous and seek to steal items from your fortresses to bring them back to their lairs.
Provided the dragon decides to make the Fort it's new lair.
-Metal Items (wood/bone stuff burns)
-Artifacts
-Gems
-Food
-Corpses
Hydra: (Again in "Jason and the Argonauts" the hydra was the guardian of the Golden Fleece)
It seems the hydra in mythology is water affiliated so perhaps if there are some dwarf made fountains or water reservoirs?
-Corpses
Roc:(I only know of the two headed Roc appearing in "The Seventh Voyage of Sinbad" which picked up the hero and carried him away to his nest.)
I had an emu once as a child and it would follow me around the yard pecking at the buttons on my shirt. We would also put marbles into water dishes of ducklings and small chicks to induce them to drink.
I do not picture the Roc making a lair inside the fortress though. Being a bird It would most likely make a nest somewhere above the fortress. Though I don't know for sure.
-Gems
-Corpses
Giants (Giant, Cyclops, Ettin, Minotaur):I would think it would be along the same lines as the dragon but would include the flammable stuff and most definitely the booze.
I'm just throwing out ideas. So please feel free to take any of these ideas and run with them (as long as they are not scissors).