Last night I ran a Reverse Dungeon in the style of the old pc game Dungeon Keepers. The players had pre generated monster characters whose job it was to take over a dungeon from a former group and continue operations. They were ordered by their lich lord master to expand the dungeon and look for new sources of wealth. The dungeon was ran by the players and I played the heroes that kept coming and adventuring every so often.
They started with the pregens and five slaves. They had a basic floor plan with no rooms completed. I made up a chart for purchasing various room types and monsters. The idea was they make a room type and at the end of the building phase they might attract monsters to pay to work for them.
Each turn was broken into a weeks worth of time . Each player character could do one action per week. Run the slaves, explore, build, study etc .
They started with 200 gold initially and built a kitchen and a small lair. The lair attracted six goblins. No pesky heroes showed up the first week. Unfortunately the goblin player pushed a few of the slaves to exhaustion and they passed out. They only made a few coin.
Week two had them building an alter room and a second small lair. The heroes bugged them but they were only first level. The monster players dispatched the heroes after a few combat rounds. Only the monsters in occupying areas were allowed to fight so as to keep from the everyone rushes to defend the dungeon even though they are busy with something else routine. As the heroes explored the dungeon the monsters got checks to notice and join the fray. The drop played by my wife turned out to be a nicer taskmaster and she allowed the exhausted slaves a rest and did not push the others. They earned a few coin from the mines and after looting the heroes and sending a few to work the mines they earned a few more coin.
Turn three had the monsters building the alter (large rooms take two weeks to complete) and they rolled an imp who offered to work for magic items found. They accepted and wrote off the gold on their books. The second pair attracted bugbears. Several players went exploring and found gold deposits. A gold mine! They were attacked again by heroes who caused some goblins to meet their maker. The heroes ended up becoming slaves in the new gold mine.
Turn four had them attracting more goblins. No heroes attacked. They put alarms on doors to alert the creatures in the lairs. The gold proved to be useful . My son purchased a water lair to attract lizard men.
Turn five had a band of heroes with their henchmen show up demanding the release of prisoners. The heroes came in all sides and the battle raged for about an hour to be concluded by the heroes being chased off or eaten by monsters. A few were pressed into service and one unfortunate was turned into a revenant vampire by the vampire player.
I made the rules for the game but it was very simple. The players had a 50% chance of obtaining 1d6 monsters for small lairs, 2d6 monsters for large lairs or one large monster, etc. Once the monster was attracted it had to be paid. Monsters are they paid monthly or there's a 50% chance that 1d6, 2d6, etc. run away. Heroes had the same chances of attacking. In all cases of percentages I had the players roll.
Rooms had a standard footprint and could be arranged as players desired. Small rooms were 4x6, large rooms were 8x6, etc.