You don't need an attorney to draw up a contract (not a work order) that lists in detail every operation, every component, and delivery time. Specify time payments by date (not interval). Now add penalties for late delivery: X dollars for every day/week/month.
It becomes binding when it is notarized as an "acknowledgement*" (in the manner required for a deed to be recorded, not sworn, not witnessed) by both parties. If it's a corporation it must include a statement that the signer had the authority to bind the corporation to contracts.
What it does: it permits you to sue him for very specific damages (the penalties) rather than hair-pulling he-said-she-said about how much is worth what.
When he lawyer sees this, he screams "what the fook is wrong with you!!!"
It doesn't need to be filed with the Court, but most County Clerks will accept a copy for a small fee (it's $25. here), so his lawyer knows you're serious.

* I'm sorry to say that although all notaries and attorneys are required to know what this is, very few of them do. You can Google it and copy the language.