Many variations of business rules have been proposed, most of them going into a lot more depth into business management. I have my own version of that:
D&D 5E - (Homebrew) Stalker0's 5e Business Rules Draft 1
My goal here is a set of rules to keep business running simple but still add a few more options for players wanting to see their business grow. The money profit on average is a bit high but again its designed for player fun and so you want to see some reasonable numbers most of the time.
Buying a Business
A business costs 100 gp for each level of the business (a 3rd level business would cost 300 gp). A business can either be "Standard" or "High Risk"
Making Money
Each quarter, a business generates profit (or loss) based on this value (the profit check):
Standard Business: (2d6 - 5) * 20 gp * Business Level
High Risk Business (1d12 - 4) * 20 gp * Business Level
Rolling the maximum value is considered a critical success, and the minimum is a critical failure (see below).
Example: A standard 3rd level business rolls 2d6 - 5 gets a 2 total. That is 2 * 20 * 3 = 120 gp, a very solid quarter.
Unsteady Business
A business becomes unsteady under the following circumstances:
- New business just starting out
- Grows into a new level (investment only)
- Is taken under new ownership
- Suffers a critical failure on a profit check.
This applies a -1 to all profit checks. The business remains unsteady until it rolls a positive profit check.
Growing a Business
A business grows to another level in two ways:
Investment: The owner spends 100 gp and rolls a profit check (gaining no money from the check). On a 0 or higher, the business gains a level and becomes Unsteady. On a failure, half of the investment is lost. On a critical success, the business gains an additional level.
Organic Growth: When a business rolls a critical success on a profit check, it may attempt to gain levels like the Investment option but with no money required. Business levels acquired this way do not unsteady the business.
DM Note: Particularly open and friendly markets may give a bonus on the investment profit check, while extremely competitive markets may give a penalty.