Ha! Just had a similar chat with someone .... someone who ought to know better.
THAT gentleman was trying to 're-invent the wheel' .... making sure it always rolled his way. Lawyers look at such folks ... giggle ... and upgrade their vacations to First Class.
Note #1: If you're planning on doing business with strangers, there is absolutely no doubt: you need a lawyer. On retainer. Available. In your area. Versed in construction practices.
Let him provide the contract.
Note #2: If you decide, in spite of my advice, to try to 'go it alone,' use a locally proven contract - and vary it as little as possible. If nothing else, have a nationally known service company come out and fix something .... then copy their contract.
"Form Contracts," such as those available at the stationery store, can vary from very good to totally inappropriate.
Learning electric work is a trade. Running a business is a trade. Law is a trade. If you haven't already taken some courses .... take them now.
