Value of existing apartment complex

[John Kabot]

Just curious how everyone establishes value of a given operating apartment complex.  I have an eight unit complex that rents for $575 a month per unit.  Built in 1977 and somewhat updated. I put a new roof, windows, paint, flooring, Appliances, and sealed the parking lot.  I was told you take the gross rent for the year ($4600 a month times 12)  add a zero to the end and that's the value.  Anybody have a more scientific method?  (Net is about $3600 a month)