Thanks, ***** ***** come back he has is to reject the goods if he claims they are inferior quality, not as described, not fit for purposes, etc. This would be under the Consumer Rights Act 2015.
He did not take your advice to instruct a builder either. I presume there was no contract other than for you to supply the materials?
He cannot simply say he wants £1,000 without justifying it or itemising this. Did you lose out financially as a result of this?
I would be inclined to tell him you dispute the £1,000 and any other losses which he is claiming for. He would need to prove that a contract existed over and above the supply of the materials.
Let me know if I can help further. If he tries to sue in the small claims court, I can help with any defence. If you could accept this answer and give me a star rating, I can offer unlimited follow up Q&A's at no extra charge