What California requires
The State's contractor board sets three rules for a home improvement contract. The down payment cannot be more than ten percent of the contract price or a fixed amount set by the State, whichever is less. The contract must carry a detailed, written payment schedule. And payments to the contractor cannot run ahead of the value of the work performed or the materials delivered, apart from the down payment.
Our agreements follow those rules; the five checks before you commit to a rebuild contractor show you how to read any contractor's schedule against them.