It's really easy for projects to go wrong. Construction is a horrible world, and it involves bits of baked earth and mud and lots of rain and and grumpy subcontractors. So it's all about how you mitigate that. Your builder ought to have indemnity insurance, of course, and liability insurance. It's imperative that your project is insured. If for some reason it all goes wrong. Look fully into insurance, a good builder won't be offended by you asking