Actually the title of this book should read 'Building the Great Stone Circles of the North' edited by Colin Richard and at £39.95 is not exactly cheap.....
There is no answer of course, "an unproductive question" as Richard points out. But looks a good read, and for a summing up this link to Orkneyjar outlines the thinking behind this based on a project set up in 2002 called - The Great Stone Circle Project.

http://www.orkneyjar.com/archaeology/dhl/papers/cr/index.html