#1: An Estimate
Ask for a free estimate on any job, and the contractor should be willing to give you a full estimate for all the work that must be done. Someone who will not give you an estimate is likely not willing to be forthright with you about the job, and you should avoid them for your own sake.
Ask your contractor how long it will take to do the work, and the estimate will helps you understand how long they need. While they cannot make provisions for the weather, you should discuss how weather may affect the timeline. Avoid anyone who will not commit to a basic schedule.
#3: Surprise Prices
Ask your contractor if they will honor the contract they give you and make sure they cannot surprise you with many fees that you simply cannot afford. They should not expect you to pay money you do not have, for a job they already agreed to.
Ask your contractor which materials they will use. The materials being used can affect the pricing. It is quite simple for you to control the cost of the job when your contractor is honest about what they plan to use. You should walk away with an estimate that details exactly what will happen at your home.