Like others have already stated, contract law is - for the most part - governed by state law. Therefore, contract law for each state may vary somewhat. However, most states' laws are based on English common law, and they also generally adopt codified laws based on the uniform code. As such, most states laws are generally the same (with notable exceptions such as Louisiana - which is based on French common law.)
The best bet is to hire an attorney who specializes in contracts - specifically, one with experience in construction contracts. However, if you can't afford an attorney right now, anything in writing is better than nothing in writing. Courts will even accept a handwritten note signed by both parties that is written in laymen's terms. So, I would suggest finding some templates online or buying a generic contract at your office supply store if you can't have a contract drawn up that meets your specific needs. Again, anything in writing is better than nothing in writing.