I just posted my thoughts on multi-family property under the "rental property" thread. When I look at potential multi-family property I evaluate it based on "cash-on-cash" return, not cap rate. I consider cap rate to be a real red herring, since it's easier to manipulate. Be especially suspicious of "pro-forma" numbers, and always demand to see the last 2 years tax returns to confirm the income and expenses. Cost per door is also pretty useless unless you're looking at a perfect apples-to-apples comparison. For me, the biggest unexpected expense was turnover. Feel free to contact me directly with any other questions.