Style of overall, not the first union staff rejected (4-5)

'style' is the definition.
(architectural style)

'overall not the first union staff rejected' is the wordplay.
'overall' becomes 'smock'.
'not the first' means to remove the first letter.
'union' becomes 'tu' (I've seen this in other clues).
'staff' becomes 'rod' (I've seen this before).
'rejected' says the letters should be written in reverse.
'rod' written backwards gives 'dor'.
'smock' with its initial letter removed is 'mock'.
'mock'+'tu'+'dor'='MOCK-TUDOR'

'of' acts as a link.