Beams following in empty rays (7)
I believe the answer is:
rafters
'beams' is the definition.
(I know this)
'following in empty rays' is the wordplay.
'following' becomes 'after' (I've seen this before).
'in' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'rays' with its middle taken out is 'rs'.
'after' inserted inside 'rs' is 'RAFTERS'.
(Other definitions for rafters that I've seen before include "Roof supports" , "Internal roof beams" .)