Additional building has former Queen cross (5)
I believe the answer is:
annex
'additional building' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'former queen cross' is the wordplay.
'former queen' becomes 'anne' (Queen Anne, 18th-century queen. I am not sure about the 'former' bit.).
'cross' becomes 'x' (an X is a cross).
'anne'+'x'='ANNEX'
'has' acts as a link.
Can you help me to learn more?
(Other definitions for annex that I've seen before include "Appropriate" , "Add as an extra part" , "Join - add" , "Attach, invade" , "Take (land) by conquest" .)