Herb, in charge of a building in Rome (8)
I believe the answer is:
basilica
'building in rome' is the definition.
(St. Peter's Basilica in the Vatican)
'herb in charge of a' is the wordplay.
'herb' becomes 'basil' (basil is a herb).
'in charge of' becomes 'ic'.
'basil'+'ic'+'a'='BASILICA'
(Other definitions for basilica that I've seen before include "Roman style of building" , "Roman building used for public administration" , "Large Christian church with two rows of columns and apse at one end" , "Bails CIA out of the large church" , "Church edifice" .)