Umbrella Insurance vs. Individual Insurance Per Building

[Eugene Gutierrez]

What is the action that triggers changing from insuring each property one-by-one to creating an umbrella policy to cover the portfolio?

I own a number of buildings in Maine and currently each building is individually insured. I am assuming that at some point it might be more cost effective to get an umbrella insurance policy on all my buildings. Currently, I have about ten buildings. 

My insurance agent has not really jumped out with an answer for me. Is Maine a tough place to get commercial real estate insurance? What has been other people's experience?