An effective DevOps organisation is only as good as the people in it. The composition of the team depends on the product under development, its maturity stage and the culture of the company. What works for Google, may not work for you.
Having said that, there are models from which to choose: each with its own advantages and disadvantages. The transition to DevOps will not occur the same way in different companies. How then do you create and effective SRE team and what common patterns are needed for it?