Roof on Stonehenge?

If one looks at how a neolithic round house is built, then posts are placed into pits in the ground and the posts are connected togther in a ring (the ring is called a “wall plate”) using a series of beams at about head height (e.g. see http://www.gallica.co.uk/celts/build.htm). It is important to have a strong “wall plate” so that the roof can be supported. When a roof is placed on the structure, the posts tend to bend outwards increasing the radius of the wall plate. This in turn puts each beam in the wall plate under tension. When one considers Stonehenge, it would appear that the lintels form a wall plate via the lintels and the mortice and tenon joints interconnecting them. However, putting stone under tension is not a good idea and would have led to a failure of the structure at some point. Is this the reason why a roof on stonehenge is generally regarded as a stupid idea? I have read various books on Stonehenge and even suggest that the stone structure of Stonehenge replicates that of a round house, but they could never have intended to have put a roof on the structure. However, the authors of these books don’t say why.

Does anyone have any others ideas?