Article removed from shed very slowly (5)
I believe the answer is:
lento
'very slowly' is the definition.
(musical term)
'article removed from shed' is the wordplay.
'article' becomes 'a' (indefinite article).
'removed from' is a deletion indicator.
'shed' becomes 'leanto' (I've seen this before).
'leanto' with 'a' removed is 'LENTO'.
(Other definitions for lento that I've seen before include "Slowly (mus.)" , "Old sayings" , "(When playing music) slowly" , "How one scores slowly" , "Scored slowly" .)