For getting a loan, they'll look at totally different scenarios for 3 units vs. 10 units. Any 4 unit or less multifamily building when qualified is similar to investing in a single home. If it's vacant, what is the condition and would you be able to afford the payments on it for x amount of months, etc. If it's occupied, the bank will want to see the rents and history of the property. At this point, along with usually looking at your credit/income/etc, they will calculate the "debt coverage ratio" among other things. The basic rule is the income AFTER expenses and vacancy must cover anywhere from 115-125% of the mortgage payments.
If you happen to aim for a larger unit building, there's a few more complication in regards to financing, simply b/ there are fewer places that are willing to finance commercial property (commercial = 5+ units). Either way you should plan on having 25-30% down payment.
My recommendation would be to find a commercial lender and maybe a local bank to discuss your financing situation further.
Jul 21, 2009