"I'm sure all this must have been discussed/printed? elsewhere"
Yes, this was also suggested by Geoffrey Grigson ie. in 'The Shell Country Book' p.73:
"Religious or secular, it is possible to think of Stonehenge as a very large roofed round house inside its enclosure, and of Avebury as a pair of roofed round houses with stone uprights inside a great circular ditch and a great stockade of stone posts, with an infilling between the posts which has long since disappeared" (Phoenix House, London. 1962)
but it does seem odd how this very reasonable idea hasn't received more critical attention. Huge wooden superstructures are routinely introduced into discussions about lifting large stones.
A few subsidiary points:
1) Stonehenge seems to have been built on - and with - an earlier prototype (perhaps originally in Pembrokeshire?). At any rate, some of the bluestones also have remnant mortise / tenon joints (indicating a similar lintelled construction) and, as there is so little bluestone dust at Stonehenge, it seems likely that these were fashioned - and probably assembled - elsewhere.
2) A good candidate for main roof timbers would be Scots pine (lightweight, available in straight lengths >20m, and present in the archaeological record at Stonehenge / Durrington etc.). It's unclear, however, where the nearest source for such large timbers might have been, since Scots pine disappears from the pollen record in lowland Britain around 6,000 BP (probably more through human clearance than by 'climate change', as popularly supposed). It's possible, therefore, that Stonehenge - and other sites - involved the long-distance movement of huge pieces of timber, in feats easily rivalling the transport of smaller (though much denser) megaliths.
3) Moving these quantities of stone and timber would have been much easier if people used draft-animals but, for some reason, reconstructions - like the farcical attempt to move a Pembrokeshire bluestone in 2000 - seem to only envisage manpower. There is, though, clear archaeological evidence of oxen at Stonehenge (in the vast quantity of shoulder-blades used as shovels) and many early depictions of animal-haulage in the near East, where these beasts were first domesticated - nb. also: pictures of oxen apparently hauling objects in the 'axe-plough' motif at Gavrinis / Table des Marchand, Brittany, and legendary association of oxen with haulage eg. at Llyn Fan Fach, Llyn Wyth Eidion, Gwyr-yr-Ychen-Bannog earthwork etc.