Decay reported beneath the Pantheon, for example (7)
I believe the answer is:
rotunda
'the pantheon for example' is the definition.
(the Pantheon in Rome is an example)
'decay reported beneath' is the wordplay.
I cannot quite understand how this works, but
'decay' could be 'rot' (rotting is a kind of decaying) and 'rot' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for rotunda that I've seen before include "Circular room or building" , "domed hall" , "Round domed building" , "Do a turn (anag) -- circular domed building" , "Circular building with a dome" .)