With heavy metal cladding, fear collapsing building (6)
I believe the answer is:
prefab
'building' is the definition.
(I have seen 'Temporary building ' mean 'prefab' so perhaps 'building' could also mean 'prefab')
'with heavy metal cladding fear collapsing' is the wordplay.
'with heavy metal' becomes 'pb' (I can't explain this - if you can you should give a lot more credence to this answer).
'cladding' indicates putting letters inside (I've seen this in other clues).
'collapsing' indicates an anagram.
'fear' is an anagram of 'refa'.
'pb' enclosing 'refa' is 'PREFAB'.
(Other definitions for prefab that I've seen before include "Sort of dwelling" , "small postwar house" , "Type of house" , "British inter-war temporary housing, popularly called" , "It's readily put together" .)