Timber and some large stones for facing walls (6)
I believe the answer is:
ashlar
'facing walls' is the definition.
'ashlar' can be an answer for 'facing' (I've seen this before). I'm not certain of the 'walls' bit.
'timber and some large stones' is the wordplay.
'timber' becomes 'ash' (I've seen this before).
'and' means one lot of letters go next to another.
'some large stones' becomes 'lar' (I can't explain this - if you can you should believe this answer much more).
'ash'+'lar'='ASHLAR'
'for' is the link.
Can you help me to learn more?
(Other definitions for ashlar that I've seen before include "Dressed stone for facing (A, not E)" , "Rectangular block of hewn stone" , "Masonry made of large square-cut stones" , "wall-facing" , "Has Lar produced squared stone?" .)