Solid farm building (6)
I believe the answer is:
stable
I believe this clue is a double definition.
'solid' is the first definition.
(thesaurus)
'farm building' is the second definition.
(stable is a kind of farm building)
(Other definitions for stable that I've seen before include "Lasting" , "Standing firm" , "Fixed; secure" , "Unchanging (condition); some racehorses" , "farm building" .)