Check cast-iron building by National Trust (10)
I believe the answer is:
constraint
'check' is the definition.
(I've seen this before)
'cast-iron building by national trust' is the wordplay.
'building' is an anagram indicator.
'by' says to put letters next to each other.
'national trust' becomes 'nt'.
'cast'+'iron'='castiron'
'castiron' anagrammed gives 'constrai'.
'constrai'+'nt'='CONSTRAINT'
(Other definitions for constraint that I've seen before include "Check" , "force" , "Limit - restriction" , "restrictive condition" , "Restriction - in contrast (anag)" .)