Barn roof spinner (4)
I believe the answer is:
vane
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">barn roof spinner</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for vane that I've seen before include "Device that rotates to show the direction of the wind" , "Weather blade" , "It shows wind direction" , "Blade of a propeller" , "Part of a weathercock" .)