Investing in apartment complexes could be one of the best ways to make extra money and build diversity into your real estate portfolio. Apartments are interesting because they allow you to enjoy the rental income, but you are not immediately dependent on just one tenant, as you would in a single-family home. Yet, there’s much to know about this type of real estate investing.Are apartment buildings on the horizon for you? As you consider the value of investing in an apartment building, it is always a good idea to make some decisions.