Be very careful

(1) get a the contract, specifying exact material, exact schedule of work, including penalty clause to say they owe you $XXX for every day of delay. Penalty clause is important, otherwise they can send worker to other jobs before finishing yours.

(2) check contractor's state license.

(3) check contractor's insurance (for its own worker's injury), if you don't have this, you are technically the worker's employer and they can sue you for injury.

(4) check contractor's bond (for its damage to your house, and in case they don't finish the job), if you don't have this, contractor can run away and you will have no insurance against it.

(5) Ask for references for previous jobs.

Don't try to save money, a deal too good to be true is, too good to be true.