Keep in mind that buildings with five or more units are usually considered commercial properties. You may have to pay a higher interest rate than for a residential mortgage property and additional fees. Before you buy a large property, think about who will manage the building. If you plan to manage it, plan to spend at least 20 hours a week as you get things up and running. If the building is in poor condition, you'll need cash to put it in better shape.
Costs go up dramatically when upgrading a large building.
A new heating system could set a landlord back tens of thousands of dollars. If you're handy, you can save money by doing your own minor repairs. Then again, you will be on call 24 hours per day. Multi-family buildings have other costs, including hazard insurance, liability insurance, grounds keeping, landscaping, trash removal, snow removal, advertising, property taxes and maintenance. The rent you charge should cover all of these, plus utilities.