Should I go as is on asking or offer 20% less

[John Corum]

Okay, I am looking at a deal where the seller is asking $455000 for a 13 unit slightly distressed apartment building. Currently bring in $6000 a month. The area cap rate ranges from 7-9%. In my numbers I am using a conservative 40% expenses mainly because I have no other information on the property. I come up with an 11% cap rate. Is this a good deal, I feel it is. Also should I still offer 20% less than the asking price? 

PS, it is owned free and clear but I don't think the guy will go for a lease option or hold first mortgage.