Builders have to buy full packs, some buy more to save time, others want 100 sq m but order 110 sq m to allow for breakages. With tiles one man can lay 500 on a job, and another guy doing the same job can lay 545.
This issue revolves around what was agreed at the contract stage, its normal for the builder to keep all the left overs, he might have reckoned on a saving of £100-00, and it keeps him happy. Clients who want the left overs are not the best clients to deal with, just pay the man and have done.
* I have had three clients like this, all had the audacity to invite me back to do more work for them and one got screaming mad upset when I said Please try Yellow Pages not us!. He actually said "it was our duty to work for him again", 6 months later I did his bosses house, a Police Supt, and just maybe he got sacked because I was told he was heavily disliked at work and my comments to his superior tied in with what everyone else in the Police Force had said about him.