If you own a large house and you have more space than you need, you might be able to turn it into apartments and rent them out.
Check local zoning regulations to find out if you would be allowed to do that.
If the answer is yes, consult a local contractor or architect to discuss what kinds of renovations would be necessary and how much they would cost.
Research the local housing market to figure out how much you could charge for rent.
Add up the costs of your mortgage, taxes, insurance and maintenance and compare that to your total potential rental income.
Some apartments might be unoccupied for long stretches of time. Figure out if you could still cover all your expenses.
Being a landlord can be a hassle. Hiring a property manager could make your life less stressful, but it would limit your profits.