Part of roof initially buckling in storm (5)
I believe the answer is:
gable
'part of roof' is the definition.
(I've seen this before)
'initially buckling in storm' is the wordplay.
'initially' says to take the initial letters.
'in' means one lot of letters goes inside another.
'storm' becomes 'gale' (a gale is a windy storm).
The first letter of 'buckling' is 'b'.
'b' put into 'gale' is 'GABLE'.
(Other definitions for gable that I've seen before include "Part of exterior wall" , "screen legend" , "American film star, d. 1960" , "US actor" , "American actor" .)