At the start of the book "The Making of Stonehenge" by Rodney Castleden (Routledge) (1993) there is this quote

And there is on this island a magnificant precinct sacred to Apollo and a notable spherical temple decorated with many votive offerings. There is also a community sacred to this god where many of the inhabitants ... worship the god with songs celebrating his deeds ... It is said that the god returns to the island every 19 years, the period in which the return of the stars to the same place in the heavens is accomplished. At the time of the appearance, the god plays on the lyre and dances continually by night from the spring equinox until the rising of the Pleiades.
Diodorus Siculus Histories Book V (50-30BC)
paraphrasing Hecateus (330BC) in what
may be the earliest documented description
of Stonehenge

Rodney Castleden comments on the word "spherical" (p240) and suggests the word implied is 'astronomical' referring to the celestial sight lines contained within the construction of the stones rather than referring to its circular shape as some have thought.

Taking an excerpt from a book with its feet firmly in the fringe (The Sphinx and the Megaliths by John Ivimy (Abacus) (1976) p91), I found that this author takes a different slant. The central postulate behind this book is that Stonehenge was built by an Egyptian colony. By quoting him I am not suggesting that I agree with any part of what he says, I am just interested in what people have had to say with the fringe idea of a roof on Stonehenge over the years.

First John Ivimy gives us a little more from Diodorus:
"Of those who have written about the ancient myths (relating to the Hyperboreans) Hecateus and certain others say that in the regions beyond the land of the Celts there lies in the ocean an island no smaller than Sicily. This island, the account contnues, is situated in the north because their home is beyond the point whence the north wind (Boreas) blows;" You can find more quotes from Diodorus on the web (e.g. "The Eternal Idol" website (including the original Greek if you prefer), where it suggests the word spherical can also mean "vaulted").

and this is how John Ivimy interprets Diodorus (warts and all!):

" The land of the Celts' (or Gauls) clearly means France, so the island can hardly be any other than Britain; and Stonehenge is the only site in Britain where the remains of a pre-Christian structure have been found which could reasonably be identified with the magnificent 'spherical' temple of Apollo. The Greek word translated here as 'spherical in shape' is sphaero-eides, which might be translated literally as 'having the appearance of a sphere or ball'. It is not possible without doing violence to the original to translate it, as is sometimes done, 'circular' meaning circular in two dimensions only. In every case where the word occurs in Liddell and Scotts lexicon it implies circularity in three dimensions. (In Greek, as in English, people sometimes said 'circular' when they meant 'spherical', but they never wrote 'spherical' when they meant 'circular'). But sphaero-eides is sometimes used to describe a hemi-spherical object such as the rounded end of a cylindrical rod or post., and it is in this meaning that the context strongly suggests the word is intended to be used in Hecataeus' description of the temple of Apollo.
On this interpretation we are driven to the conclusion that either the Greek historian was guilty of an error of fact, or Stonehenge was at one time covered by a hemispherical dome. At first sight, the former seems more probable, but it is never wise to dismiss factual statements in history books as fabrications simply on the ground simply that they cannot be made to fit in with current theories. The only reason why the idea that the Stonehenge temple might once have had a domed roof has never been seriously entertained by archaeologists is that the construction of a dome would obviously have been beyond the capacity of the neolithic people by whom they maintain the temple was built.
Once it is conceded that the builders may have been civilised, intelligent, and well organised people, the roofing of Stonehenge by means of a dome over the whole structure without internal support becomes a practical possibility. Just such a dome was built by the Mormons to roof their Tabernacle in Salt Lake City in the 1860s, when they were hundreds of miles distant from civilisation. It is an oval structure 250 feet by 150 feet with no interior pillars, made entirely of wood without the use of metal, even for nails. A dome over Stonehenge would have been easier to build than the Moromon Tabernacle because it would have been circular and smaller, say 140 feet in diameter. In bothe cases the building would have been carried out largely by unskilled labour inspired by a sense of purpose derived from religious faith.
One piece of archaeological evidence seems at first sight to be consistent with this idea. The 'Y' and 'Z' holes, dug some time after the last sarsen stones had been erected, are placed where we might expect to find the foundations of the wooden structure that supported a dome. Atkinson says the holes were never used to support megaliths, but that does not mean that it can be proved that they could not have held stout wooden pillars like those that were used to support heavy masonry in the Palace of Minos in Cnossos - tree trunks erected upside down, tapering downwards, placed either in a flat stone plinth or directly on solid ground without one."

It would seem that John Ivimy never discovered the article by Vayson de Pradenne, the prouncements of Joseph Lockyer or the opinion of Dr John Thurnam all of which would have backed his argument. Although the suggestion that the Y and Z holes may have been the remains of post holes for a roof predates Bruce Bedlams model, but it is not the first time that these holes have been considered as the remains of supports for a now vanished structure.