There seems to be scant information regarding what the inside of a Greek temple would have looked like in its heyday. Is there any scholarly consensus as to what these marbleous buildings would have looked like on this inside?
Are there any historical sources / academic works which adequately describe the interior of these buildings when they were first built?
Although most Greek temples are preserved, if at all, as shells, we have a fairly good idea of what their interiors looked like.
Virtually all Greek temples consisted of an enclosed room (cella) surrounded, or at least fronted, by a colonnade. The colonnades of many Greek temples have survived. The cella, however, has often disappeared, for a simple reason: stone robbing. Throughout the Mediterranean world, later builders cannibalized Greek and Roman buildings for their stone. Columns were hard to pull down, and their drums were awkward to reuse. The squared blocks that made up the walls of a cella, on the other hand, were easily re-purposed, and so tended to be spirited away.
A few exceptionally well-preserved temples still have their cellas. The most famous is the Temple of Hephaestus in Athens, which is virtually intact. Though the interior was modified when the temple was converted into a church, its layout is still easily discernible. Another excellent example is the Temple of Concord at Agrigento in Sicily, likewise preserved by being converted into a church.
These buildings, of course, preserve only the bare walls of the interior. In antiquity, they would have been dominated by a cult statue (often colossal) of the god to which the temple was dedicated. The rest of the dim and musty interior would have been heaped with centuries of offerings to the god. Unlike churches or mosques or synagogues, temples were not congregational buildings; all the religious action (i.e., sacrifices) happened outside, usually at an altar near the front porch. Temples were conceived, basically, as a combination of dwelling for the god and storehouse for the god's belongings. Their doors were open during sacrifices, so that the god's statue could "see" his worshipers making their offering; but only occasionally were visitors allowed inside.
We do, however, have a few descriptions of temple interiors, many provided by Pausanias, who wrote his Description of Greece, a sort of proto-travelogue, in the second century CE. Pausanias provides a particularly lengthy account of the Temple of Zeus at Olympia, which contained a famous cult statue of the god. He begins by describing the statue:
"The god sits on a throne, and he is made of gold and ivory. On his head lies a garland which is a copy of olive shoots. In his right hand he carries a Victory, which, like the statue, is of ivory and gold; she wears a ribbon and – on her head – a garland. In the left hand of the god is a scepter, ornamented with every kind of metal, and the bird sitting on the scepter is the eagle. The sandals also of the god are of gold, as is likewise his robe. On the robe are embroidered figures of animals and the flowers of the lily." (5.11.1)
After elaborating at length on the statue and its setting, he notes that the floor of the cella is paved with black and white marble, proceeds to list some of the many votive offerings heaped along the walls. A translation of the whole passage may be found here.