In the middle of Warsaw, following beams (7)
I believe the answer is:
rafters
'beams' is the definition.
(rafter is a kind of beam)
'in the middle of warsaw following' is the wordplay.
'in the' means one lot of letters goes inside another.
'middle of' says to take the centre.
'following' becomes 'after' (following can mean after or as a result of).
The centre of 'warsaw' is 'rs'.
'rs' enclosing 'after' is 'RAFTERS'.
(Other definitions for rafters that I've seen before include "Internal roof beams" , "Roof supports" .)