Buildings requiring a hundred new slates (7)
I believe the answer is:
castles
'buildings' is the definition.
(I've seen this before)
'a hundred new slates' is the wordplay.
'a hundred' becomes 'c' (Roman numerals).
'new' indicates anagramming the letters.
'slates' anagrammed gives 'astles'.
'c'+'astles'='CASTLES'
'requiring' is the link.
(Other definitions for castles that I've seen before include "English homes?" , "Fortresses" , "buildings" , "Rooks" , "Keeps" .)