Plain site, green building (9)
I believe the answer is:
serengeti
'plain' is the definition.
(I know that Serengeti is a plain)
'site green building' is the wordplay.
'building' indicates an anagram.
'site'+'green'='sitegreen'
'sitegreen' with letters rearranged gives 'SERENGETI'.
(Other definitions for serengeti that I've seen before include "area of the plain" , "Tanzanian plain renowned for its wildlife" , "Wildlife-rich region of Africa" , "Tanzanian national park area" , "Green ties (anag.)" .)