They're provided for the rest of the layers (6)
I believe the answer is:
roosts
'layers' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe there's a link between them I don't understand?
'they're provided for the rest of' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'of' could be 'o' and 'o' is found in the answer.
The remaining letters 'ross' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'the' acts as a link.
Can you help me to learn more?
(Other definitions for roosts that I've seen before include "So sort out for birds' perches" , "Where birds settle to sleep" , "Stays" , "Perches for domestic fowl" , "Of bird, settles for sleep" .)