The only thing that really matters is whether he's putting value on the house. At the moment I'm getting paid for 10 grands worth of work and putting 35 grand on the value of the house. Who cares what breaks I choose to take?
If you want to get paid 35 grand for your work, it rather sounds like you should stop working for other people who pay you 10 grand, and instead buy a house, do 10 grand of work on it and sell it for a 35 k uplift, right?
But then, the more I think on it, the more I think your argument makes no sense at all. It's almost as if you feel you should be entitled upfront to some of the uplift in value an asset you've improved might make if it were ever to sell. How about we remove the upfront aspect and instead promise you 50% of the change in value when the asset is sold?
If the homeowner sells for 35 grand more then bully for you, you get 17.5K. If the market takes a dip and the owner sells at a loss, you have to shoulder some of the loss too (because payment for the job was effectively giving you a share in the asset to 50% of the value it is claimed to be improved by).
I highly doubt you'd take that risk, so instead your money comes from "safe" investment - you get paid X for the work you did, whatever the change in asset value, and the homeowner who takes the risk on the value of his home also takes a risk on getting a punch on the nose if there's a market crash. It's the homeowner who's entitled to the rewards, not the builder