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 an association between them that I don't see?
'on great housing unit' is the wordplay.
'on' means one lot of letters go next to another.
'great' becomes 'fab' (short for fabulous).
'housing unit' becomes 'pre' (I can't justify this - if you can you should give a lot more credence to this answer).
'fab' 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" .)