Facing of plaster on great housing unit (6)
I believe the answer is:
prefab
'facing of plaster' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'on great housing unit' is the wordplay.
'on' says to put letters next to each other.
'great' becomes 'fab' (short for fabulous).
'housing unit' becomes 'pre' (I am not sure about this - if you are sure you should believe this answer much more).
'fab' put after 'pre' is 'PREFAB'.
Can you help me to learn more?
(Other definitions for prefab that I've seen before include "modular design?" , "Sort of dwelling" , "Factory-made building" , "Building manufactured by assembling pieces" , "Simple construction" .)