Rubbish written about very large place where birds rest (5)
I believe the answer is:
roost
'place where birds rest' is the definition.
(I've seen this before)
'rubbish written about very large' is the wordplay.
'rubbish' becomes 'rot' (both can mean nonsense).
'written about' is an insertion indicator.
'very large' becomes 'os' (abbreviation for oversize).
'rot' placed around 'os' is 'ROOST'.
(Other definitions for roost that I've seen before include "Temporary resting-place" , "Night spot for birds/bats" , "Rest on a perch" , "Colony of bats; perch" , "Place where birds rest" .)