Farm building sheltering old nobleman (5)
I believe the answer is:
baron
'nobleman' is the definition.
(baron is a kind of nobleman)
'farm building sheltering old' is the wordplay.
'farm building' becomes 'barn' (barn is a kind of farm building).
'sheltering' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'barn' going around 'o' is 'BARON'.
(Other definitions for baron that I've seen before include "Minor peer" , "British peer; business mogul" , "Husband" , "Titled man for a portion of beef" , "An English lord or a magnate" .)