Google is a decent place to start with master service agreements but one thing I learned the hard way is if you want it to be proper you need to review it with a lawyer. Every country/state has different laws regarding contracts and a contract from someone in Ohio may not be legally valid in Michigan. I had a contract with a client who didn’t pay up and it turned into a mess. Even though he had signed a contract certain parts were invalid and although it certainly helped to have something (even a simple signed piece of paper saying I agree to pay you $xxx by XX for XXX work completed).
At the end of the day the lawyer fees and the negotiated settlement amount ended up being basically a wash, but I suppose it was a valuable time to learn the lesson.