Descriptive notice

Hi,
If you speak french, maybe more people will be available to help you here as it's a french forum. But I'll try something.

The builder cannot change the contract as he wish. The descriptive notice of the CCMI is a contract that you paid for.
You can contact the AAMOI (aamoi.fr, I don't know if they help in english) that is specialized in CCMI. Members of the AAMOI can help you review the contract and help you to defend your interests.

The builder owes you what is described in the contract, at the price of the contract. You have to pay for each step completed (it's also described in the contract). When the builder as you to pay, you can ask (and he cannot refuse) a construction site visit to validate that the step is completed, prior to any payment. If the step isn't finished, you don't have to pay until it's finished. It also can be punished by law for the builder to issue an invoice in advance.

My best advisory is to subscribe to AAMOI (120€ for a year), as they can help you debunk the lies of the builder, what isn't normal or what is illegal in your contract, and to help you to communicate with your builder.