Plain green site being redeveloped (9)
I believe the answer is:
serengeti
'plain' is the definition.
(I've seen this before)
'green site being redeveloped' is the wordplay.
'being redeveloped' indicates anagramming the letters.
'green'+'site'='greensite'
'greensite' with letters rearranged gives 'SERENGETI'.
(Other definitions for serengeti that I've seen before include "Wildlife-rich region of Africa" , "Green ties (anag.)" , "place to watch game" , "area of Tanzania" , "Huge plain in Tanzania" .)