Acceptable as it's rebuilt next to the plant (12)
I believe the answer is:
satisfactory
'acceptable' is the definition.
(I know that acceptable can be written as satisfactory)
'as it's rebuilt next to the plant' is the wordplay.
'rebuilt' indicates anagramming the letters.
'next to' is a charade indicator (letters next to each other).
'the plant' becomes 'factory' (I am not sure about this - if you are sure you should believe this answer much more).
'as'+'its'='asits'
'asits' anagrammed gives 'satis'.
'satis'+'factory'='SATISFACTORY'
Can you help me to learn more?
(Other definitions for satisfactory that I've seen before include "Fulfilling expectations" , "Fully acceptable" , "Acceptable - adequate" , "Good enough" , "fine" .)