An interesting quote from a long time ago can be found in:
Stonehenge and its barrows by William Long Esq M.A., F.S.A.(from the Wiltshire Archaeological and Natural History Magazine vol xvi) printed by H.F and E. Bull, 4 St John Street, Devizes, 1876. p67

"One more theory in connection with the construction of Stonehenge must be mentioned. Four or five years ago the writer was astonished at hearing his friend Dr Thurnam give utterance to what he then considered and still considers to be, a rank archaeological heresy; viz., that Stonehenge was at one time covered with a roof. He said nothing in proof or support of this opinion, and the writer thought it might have been a passing fancy, and that it was not based on any serious considerations. As however the writer finds the following in Lieut. Oliver's paper on Prehistoric Remains in Brittany, read to the Ethnological Society, January 10th, 1871, he cannot but suppose that the Doctor attached importance to this view, and had propounded it to others: "Dr Thurnam has given up the ophite or dracontium theory as untenable, but considers that some of the circles, Stonehenge, for instance, may have been covered in with a roof, as the Scandinavian temples are represented as covered and enclosed structures. A similar idea occurred to a gentleman, who, on looking at Mr Lukis' plans of the circles and lines, suggested that the avenue might have been covered in with timber and earth, and formed long chambers for the tribe to live in, the chieftains occupying the western circular chamber."
That one so cautious, so careful and so painstaking in the examination of theories of others, should have committed himself to such an opinion as this, is, to the writer, strange indeed."

Dr John Thurnam was a reknowned antiquarian known for his work in studying barrows. His work is still quoted. It is interesting to note that the idea of a roof on Stonehenge was regarded as heresy at this time - perhaps because so many people uneducated in the science of archaeology had expressed the view and genuine archaologists were tired of answering the question. Clearly the idea of a roof on Stonehenge was widespread among the "fringe" in the mid 19th Century.