Possibly does without roof of tower block (5)
I believe the answer is:
deter
'roof of tower block' is the definition.
'deter' can be an answer for 'block' (I've seen this in another clue). I am not sure about the 'roof of tower' bit.
'possibly does without' is the wordplay.
'possibly' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'does' becomes 'deer' (I've seen this in another clue).
'without' means one lot of letters goes inside another.
't' going into 'deer' is 'DETER'.
Can you help me to learn more?
(Other definitions for deter that I've seen before include "Check" , "Discourage or prevent from doing something" , "Put off (from an action)" , "Inhibit" , "Discourage through fear of consequences" .)