Roofing material which covers church (6)
I believe the answer is:
thatch
'roofing material' is the definition.
(thatch is a kind of roofing material)
'which covers church' is the wordplay.
'which' becomes 'that'.
'covers' says to put letters next to each other.
'church' becomes 'ch' (common abbreviation).
'that'+'ch'='THATCH'
(Other definitions for thatch that I've seen before include "Old-fashioned roof covering material" , "Old-fashioned roofing material" , "Traditional material for covering" , "Organic material for old rustic roof" , "Old roofing material" .)