Relating to the side of a taller building (7)
I believe the answer is:
lateral
'relating to the side' is the definition.
(I've seen this before)
'a taller building' is the wordplay.
'building' indicates anagramming the letters.
'a'+'taller'='ataller'
'ataller' is an anagram of 'LATERAL'.
'of' acts as a link.
(Other definitions for lateral that I've seen before include "Sidelong" , "This kind of thinking is unconventional" , "Sort of thinking" , "Sideways, like creative thinking" , "Edgeways" .)