It would all depend on what the functional purpose of the dungeons was.
- If they are true dungeons - jail cells attached to a keep - then I would expect 80% of the cells to be filled, but only about 10% of the other rooms.
- If they are living quarters for a tribe of orcs, then probably only about 1/3 of the rooms would be occupied - and many would be with small groups of non-combatant types, but there'd be at least one major common room with enough of them to swarm over you in a second. They also are likely to have pets/guardian creatures
- If they are caves that certain beasts have taken refuge in then expect very few rooms with one major beast type and other creatures that would benefit from a symbiotic relationship with that creature.
- If it is a stocked dungeon by some powerful being/race and intended to be used for the sport of watching their pets destroy victims - then probably a higher percentage
I am sure there are plenty of other reasons for dungeons, but it really does come down to what the purpose of the space is... and it's not so that heroes can come and clean them out looking for treasure and gaining experience.
I keep my SFS*
storyfirststupid note at the top of every dungeon or adventure I write to remind me what will make the adventure the most fun for the party.
Here are the last 4 dungeons I ran and what the purpose was.
#1 Was the crypt of a mad archmage then lich who's lich form was finally defeated and who was the last known possessor of the artifact the party was seeking. He was horribly evil and knew people would be coming for the artifact should he ever perish so he designed his entire tomb as an inescapable trap to ensure that NO ONE would ever get the item from his cold bony fingers. What lives in a 10,000 year old tomb? Well only things that don't need sunlight, food, or water - ie, undead, demons, elementals, and the occasional nasty insect who can creep in and out via their own methods. The party was spot on in this adventure and got the artifact with minimal damage. They solved 16 riddles flawlessly... not easy ones either.
#2 Was the Castle of a Frost Giant Warlord... loaded with hundreds of giants between level 20 and 35. This adventure was brutally difficult for the characters because any more than 3 or 4 giants at a time was pretty much "instant death" I kept a chart of who was where and the party had to be extremely diligent about when they picked a fight and where. In the end the party managed to kill the king and grab his sceptre (the reason for being there) but alerted too many guards and had to have an emergency teleport out before they ever got a chance to even glance at the treasure! Not a happy party after that one. Especially since two party members teleported into the side of a cliff taking several E disruption criticals before expiring unpleasantly. Ouch.
#3 Was a rescue. The enemy had kidnapped the sister of one of the main party heroes and was holding her in their secret cave network beneath a giant waterfall. Again this was loaded with an entire raiding band of Dark Elves complete with a few demon guardians. The characters handled this by using their stealth members to locate the sister, plant magical charges at key points of the cave.... then they created a diversion, grabbed her, and ran for their lives - setting off the explosion which collapsed the cave network just in time. Again they were not especially greedy and were content to come back a few weeks later with appropriate help to sift through the rubble and claim any trinkets that had not been destroyed or lost in the river.
#4 Was an ancient crypt located in the sewer network in the OLD city that had a newer city built atop it. The party had to research old city records for weeks, track down clues, unwravel family mysteries and riddles, buddy up to a hunchback, find a missing grave in a huge graveyard and, play grave-robbers in order to find the map and then spend days crawling through foul sewers full of nasty critters just to get to the crypt - which was quite small and only populated by iron golems (they were the guardians of the item the characters sought).
Most of the items the characters were seeking were parts of a greater magic item. I often break artifacts in my world into "pieces" - as I very much liked the storyline in the Earthsea trilogy with the broken ring.
Anyway, that's just how I do dungeons and it works on the players I have gamed with through the years.
