They build a nest on moss perhaps (11)

I believe the answer is:

stonemasons

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'they' is the definition.
Both the definition and answer are plural nouns.
Maybe there's an association between them I don't understand?

'a nest on moss perhaps' is the wordplay.
'perhaps' indicates an anagram.
'a'+'nest'+'on'+'moss'='anestonmoss'
'anestonmoss' anagrammed gives 'STONEMASONS'.

'build' is the link.

Can you help me to learn more?

(Another definition for stonemasons that I've seen is " Craftspeople".)

I've seen this clue in The Globe and Mail.

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