Building for sale around castle outside (8)
I believe the answer is:
alfresco
'castle outside' is the definition.
'alfresco' can be an answer for 'outside' (I've seen this before). I'm not certain of the 'castle' bit.
'building for sale around' is the wordplay.
'building' indicates an anagram.
'around' becomes 'c' (abbreviation for 'circa').
'for'+'sale'+'c'='forsalec'
'forsalec' is an anagram of 'ALFRESCO'.
Can you help me to learn more?
(Other definitions for alfresco that I've seen before include "out of the house" , "In the open air" , "Open-air" , "exposed to the fresh air" , "Meal eaten in the outdoors" .)