Crowds of men housed in rickety shed (6)
I believe the answer is:
hordes
'crowds' is the definition.
(horde is a kind of crowd)
'men housed in rickety shed' is the wordplay.
'men' becomes 'or' (military abbreviation for Other Ranks).
'housed in' indicates putting letters inside.
'rickety' indicates anagramming the letters.
'shed' with letters rearranged gives 'hdes'.
'or' going inside 'hdes' is 'HORDES'.
'of' is the link.
(Other definitions for hordes that I've seen before include "Many" , "large numbers" , ".Shored up with crowds" , "Vast multitudes" , "Bands" .)