Size of former temporary accommodation (6)
I believe the answer is:
extent
'size' is the definition.
(I've seen this before)
'former temporary accommodation' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'temporary accommodation' becomes 'tent' (I've seen this before).
'ex'+'tent'='EXTENT'
'of' acts as a link.
(Other definitions for extent that I've seen before include "Length" , "Degree - amount - scope" , "Area something covers" , "Bulk - compass" , "The size or scale of something" .)