The most common and most likely answer to this crossword clue is the 7 letter word SLATING
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The straight part
We know that "roofing material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case roofing material = slating.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SLATING mean?
SLATING verb- To cover with slate.
- To criticise harshly.
- To schedule.
- To anticipate or strongly expect.
- To set a dog upon (a person).
- Slates collectively.
- Material for slating.
- A harsh criticism.