There are so many problems with the idea of a roof, what happens to the rainwater run-off? Excavation has found no erosive areas in the chalk around the outside nor any cut drainage channels. Why build a central Trilithon array with opposing pairs having tops at different height? If a huge roofed structure was what they wanted it would surely have been done in have been in timber; why block the interior with huge uprights when post would have done? Why dig pits as deep as 8ft to hold stones that weigh up to 45 tons to have them inside a roofed building. It simply doesn’t make sense. Stonehenge is clearly a master work of prehistoric stone architecture that was designed to be open and seen as such, for whatever ‘purpose’. Have a look at the blog on http://sarsen56.wordpress.com/ a lot of old ideas look a bit insecure.