Traditional cedar shake roofs are great roofs and need to be maintained correctly. A common issue that I have found over the years is that as cedar shake roofs age the shakes cup and lift up. Cedar shake roofs are installed on what is called skip sheathing and long story short have gaps in the sheathing below the cedar shake material. When the roof material cups and the shakes lift it opens a door for rats to come through. If I am doing an inspection on a house with a cedar shake roof I am not surprised when I get in the attic and find that the insulation has been damaged by rodent intrusion.
I was in an attic once and the insulation had been completely destroyed by rodent intrusion. I finished the inspection, explained the issues to the clients, wrote my report and moved on. A few days later the agent called and said the sellers response was: “There are no rats in the attic, we have dogs!” The reality here is that your dogs do not live in the attic. Whether you have dogs or cats it makes no difference, rats are entering your house not through the front door. Most of the time I find that they are entering through the roof system somewhere and through a hole that most people thinks is too small for a rat to get through. Your average NW rat needs a 3/8” gap to squeeze through.