We have a player that is interested in setting up a business as a moneylender, and another that wants to open a brothel. Are there official rules for this kind of gameplay? If so where can I read up on the specifics? If not, is there some kind of homebrew set of rules that I might be able to use?
Yes, see the DMG, p 127.
There is no brothel, but the closest version, a city side inn, costs 10 gp a day, and requires 5 skilled hirelings and 10 unskilled hirelings.
A moneylender sounds like a shop, which costs 2gp a day, and requires just one skilled hireling.
You then roll a 1d100, plus any days spent in downtime on it, up to +30, and earn an approproiate amount of money based off the table there.
If 1-20, you must pay 1.5 times the maintenance cost, if 21-30, 1 times the maintenance cost. If 31-40, half the maintenance cost. If 41-60, no cost, if 61-80, 1d6*5 gold pieces, if 81-90, 2d8*5 gold pieces, if 91-100, 3d10*5 gold pieces.
Any unpaid debts add -10 to the roll.
Notably, for many players this isn't satisfying. Owning a larger business doesn't increase profits at all, and such businesses are very subject to failure.
The article "5e Dungeon Masters Guide: The Paradoxical Economy of D&D" by Blog of Holding suggests some house rules to fix this:
Every week, you make a roll to see how much money your business makes (or loses). You make this roll regardless of whether you are spending your downtime running the business or not. One of the NPCs on your staff is assumed to be managing the business if your PC is not available. The DM may elect to make this roll in secret and inform you of the results when you return from adventuring. Absent other factors, the DM determines how trustworthy the NPC is, so PCs are advised to hire NPCs they already trust to run their business for them to avoid embezzlement.
Replace the 61-80, 81-90 and 91+ results with the following:
- 61-80: You cover your upkeep and make 100% of your upkeep each day in profits (since businesses make a roll every week, you are multiplying your upkeep times 7).
- 81-90: You cover your upkeep and make 200% of your upkeep each day in profits.
- 91+: You cover your upkeep and make 300% of your upkeep each day in profits.
If you spend a week of downtime running your business, you get a +10 bonus on your roll that week. If you only spend a few days running the business during the week, you get a +1% bonus for every day you spent running the business (so it’s much more efficient to dedicate an entire week).
As per normal rules, if you roll poorly and are required to pay upkeep but elect not to do so, subsequent rolls take a -10 penalty until you pay your debt. This effect is cumulative, so if you fail to pay your upkeep two times, you take a -20 on the roll, and so on. A PC may elect to leave funds behind to pay their debts if the business loses money while they are away; again if the NPC managing your business is not trustworthy, the DM may determine that they abscond with the money (tracking down an unscrupulous NPC could be an adventure in itself!).
The DM may grant other temporary or permanent bonuses or penalties to these rolls as makes sense for the story. For example, perhaps one week there is an important festival in the town, and so the DM grants a +10 bonus. Or maybe a plague hits the town, and so the DM gives a -10 penalty. Alternatively, if an important rival is eliminated or a lucrative trade deal is established, the DM may grant a +5 or +10 bonus to rolls as long as that bonus remains in effect (which could be indefinitely).