It will be regularly used as part of roof (4)
I believe the answer is:
tile
'part of roof' is the definition.
(I know that tile is part of roof)
'it will be regularly used' is the wordplay.
'regularly used' indicates alternate letters (letters selected on a regular basis).
'it'+'will'+'be'='itwillbe'
The alternating letters of 'itwillbe' are 'TILE'.
'as' acts as a link.
(Other definitions for tile that I've seen before include "Thin slab of ceramic or slate" , "Ceramic slab for roofs, walls, floors etc" , "Ceramic rectangle" , "9 for the roof?" , "Thin slab of fired clay" .)