The aforementioned thing above church, covering for roof (6)
I believe the answer is:
thatch
'covering for roof' is the definition.
(as in a thatched roof)
'the aforementioned thing above church' is the wordplay.
'the aforementioned thing' becomes 'that' ('that' can refer to something just mentioned).
'above' means one lot of letters go next to another.
'church' becomes 'ch' (common abbreviation).
'that'+'ch'='THATCH'
(Other definitions for thatch that I've seen before include "Material used to cover" , "Rural roofing" , "Old fashioned rural roof covering" , "Alternative to lead roof" , "Plant stalks as roofing material" .)