A building of marked value? (4)

I believe the answer is:

hall

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'a building' is the definition.
(hall is a kind of building)

I don't understand the remainder of the clue.

(Other definitions for hall that I've seen before include "Foyer" , "Vestibule, lobby" , "Auditorium" , "Large country house" , "See 1" .)

I've seen this clue in the Evening Standard.

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