Allowing buildings to be leased (7)
I believe the answer is:
letting
'allowing' is the definition.
('let' can be a synonym of 'allow')
'buildings to be leased' is the wordplay.
'buildings' becomes 'ting' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to' says to put letters next to each other (I've seen this in other clues).
'be leased' becomes 'let'.
'ting' after 'let' is 'LETTING'.
Can you help me to learn more?
(Other definitions for letting that I've seen before include "property for temporary occupants?" , "Granting to a tenant" , "Giving permission to" , "Renting out; allowing" , "Leasing (a property)" .)