Fountains perhaps originally assembled by builders each year (5)
I believe the answer is:
abbey
'fountains perhaps' is the definition.
(Fountains Abbey is an example)
'originally assembled by builders each year' is the wordplay.
'originally' indicates taking the first letters.
'year' becomes 'y'.
The initial letters of 'assembled by builders each' is 'abbe'.
'abbe'+'y'='ABBEY'
(Other definitions for abbey that I've seen before include "Monks'/nuns' building" , "eg Bath, Fountains" , "Religious house" , "Monastery" , "Large church" .)