At some point, characters may aspire to more than just the list of activities given. They may wish to purchase a house or land, raise troops, start a religion or a construction project. Such activities may not be done on their own without attracting the attention of rulers who will go to great lengths to stop such activities. So how to accomplish them?
Get permission, of course!
Easier said then done. In order to acquire leverage, you may go the route of "find someone who wants a quest done, and use the completion of that quest to get your favor" and that's fine and traditional. But what if you have a campaign in media res with more side quests then you can already track? What if players want to change an existing structure instead of building a new one?
Enter the concept of influence.
InfluenceThere are only a few areas of influence. Commerce/Economic, Military Power, Nobility, and Arcana/Religious. For every 1,000 people in a city, there is one 3x3 board of minor influence. For every 10,000 people in the city, there is one 3x3 board of major influence. For every 100,000 people in the city, there is one 3x3 board of grand influence. Waterdeep for example, has a population of 130,000, providing one grand board, 13 major boards, and 130 minor boards. Most cities will be much smaller than Waterdeep.
Note that there are only 9 squares on a board, and always at least 10 factions who want placement on it.
Players cannot see the influence boards, and have no idea before they act what the boards look like. A player may spend one month, with a successful relevant skill roll (spying, survival (urban), etc.) to determine the status of one minor board, which they can then see. One person devoted to the task each month enables them to continue to keep abreast of what is happening on the board.
A character may spend 1,000 gold and 1 week gaining one square of minor influence. This represents politicking, meeting people, public works, intimidation, advertising, etc.–whatever generates influence. If more than 5 squares on a board are acquired two things happen. They gain a point of leverage for that level (minor, major, grand) and they are granted one square of influence on the next highest board. If a character possesses at least one point of minor leverage, they may spend 10,000 gold and 1 week to gain a square of major influence.
The relevant skill is rolled (bureaucracy, survival (urban), arcana, religion, persuasion, history, etc.) depending on the type of influence one wishes to acquire. This determines the order everyone selects influence. Then Dungeon Master adds their influence to a board at the end of a week in the order that they were rolled.
Players may also attempt to acquire influence from other actors also already on the board. They do this by individual negotiations with the person possessing the influence. Consider that the possessor of that influence will expect or fear loss of somewhere between 1,000-5,000 gold pieces of value per point of influence acquired. (This doesn't necessarily have to be in money. Blackmail, threats, completing tasks, etc. can all be used).
At the end of the month, all factions on all boards of all levels, remove one square of their influence. There is a 1 in 10 chance per board that it is completely cleared (due to a death, random event, or change in power structure).
Boards are, in general, filled before the player characters arrive. You do not have to play out every actor in the city, though if the characters have an ally or a foil or nemesis, they may work to block the character's progress. Certain positions (harbormaster, noble, merchant, priest, captain, general, etc.) automatically grant one point of minor leverage every month, without board positions. They may translate this minor leverage into selecting influence squares.
Or, the leverage may be spent. Note that for many of these, it is required that you spend the leverage each month to maintain the benefit.
Minor Leverage: Own or run a business employing up to 10 people. Purchase or sell trade goods in bulk.
Major Leverage: Make large purchases (>100,000 gp). Own a trading vessel. Own or run a business employing up to 100 people.
Grand Leverage: Own or run a business employing unlimited people.
Minor Leverage: Employ more than 10 hirelings. Have someone arrested. Have someone freed.
Major Leverage: Employ mercenaries.
Grand Influence: Request military aid.
Minor Influence: Purchase existing property.
Major Influence: Purchase land or build new property. Acquire a standard for an informal group or company. Gain a minor title.
Grand Influence: Form an official guild. Become a member of the nobility.
Minor Influence: Practice magic in the city.
Major Influence: Gain a license to employ magic commercially. Gain a license to have a group of religious followers.
Grand Influence: Be allowed to construct a school or church (must also have nobility influence to be allowed to do so)
Obviously such a system is both abstract and scaleable. But in the use case of cities, this influence is almost always associated with a faction. "The player character party", "the thieve's guild/mob" "noble faction A", "the traders' guild", etc.
It is expected that players may be able to influence one or two minor boards themselves, but it will be necessary to ally with other major influencers in order to acquire major leverage.
Because power corrupts, society's demands for moral authority and character increase as the importance of the position increases. -John Adams