Design trendy shelter (6)
I believe the answer is:
intent
'design' is the definition.
(I know that aim can be written as intent)
'trendy shelter' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'shelter' becomes 'tent' (canvas shelter).
'in'+'tent'='INTENT'
(Other definitions for intent that I've seen before include "Firm - plan - steadfast - purpose" , "wrapped up" , "With mind fixed on purpose, concentrated" , "Concentrating on a particular purpose" , "Purpose, design" .)