Unoccupied cottage on cliff in demand (6)
I believe the answer is:
scarce
'in demand' is the definition.
(scarce can mean rare or in demand)
'unoccupied cottage on cliff' is the wordplay.
'unoccupied' suggests removing the centre (remove the inside letters which occupy the word).
'on' means one lot of letters go next to another.
'cliff' becomes 'scar' (I've seen this in another clue).
'cottage' with its middle taken out is 'ce'.
'ce' put after 'scar' is 'SCARCE'.
(Other definitions for scarce that I've seen before include "Common? Definitely not" , "Few and far between" , "Not often found" , "Not plentiful, in short supply" , "exceptional" .)