One of those awfully good fellows in the building (5)
I believe the answer is:
brick
'building' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for brick that I've seen before include "dropped?" , "Clay building block" , "Good guy" , "Building material" , "Rectangular block for building" .)