Unfortunatelly i just knew since about 2 years ago, until i remember.
I saw in directory of creations https://3dwarehouse.sketchup.com many great jobs (of many media contents like: The Lord of the ring, Marvel and DC comics, The Simpons, Back to the future, etc). Maybe some of that could be used in Hero Quest adventures. Specifically about HQ i didnt find.
Compared to 3DS Max Sketchup is softer than and as easy as (or easier) and to handle too.
To download and explore that jobs just need to install Sketchpad and open the file. There are free versions (to student and other, if I'm not mistaken) is more limited, even so is great.
So it could be used by members here to build things to HQ.
SAMPLES
Castles
https://3dwarehouse.sketchup.com/search.html?q=castle



Dungeons
https://3dwarehouse.sketchup.com/search.html?q=dungeon

RPG scenarios and items
https://3dwarehouse.sketchup.com/collection.html?id=fba404f7d256b16290eed24d90155e1

Medieval city
Castles
Some "The Lord of the rings" places
Ship (pirates, etc)