It's my belief there are people in the building (8)
I believe the answer is:
tenement
'the building' is the definition.
(tenement is a kind of building)
'it's my belief there are people' is the wordplay.
I cannot quite see how this works, but
'people' could be 'men' (men are people) and 'men' is found in the answer.
'belief' could be 'tenet' (synonyms) and 'tenet' is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tenement that I've seen before include "Run-down dwelling housing many people" , "Piece of owned land" , "(Scottish) building comprising separate flats" , "Run-down building housing many people" , "Apartment in a US block" .)