I'm doubtful that you would get additional compensation in your hypothetical example.
You're not worse off if you didn't spend anything and you are half-way towards your goal of having a house.
You're not worse off if you didn't spend anything and you are half-way towards your goal of having a house.
Contractors hate taking over someone elses' half-done work, as they now have to deal with someone else's shortcuts without knowing what they are.
(This goes both ways, of course - if I back off the deal and have the contractor stop all work, I usually have to pay in full anyway.)