Start with a plan and ideas. You will get a more accurate quote.
People who have done similar builds are your best resources.
Get 3 bids. Ask a lot of questions and get a written bid from each one.
The best folks are the busy ones.
Ask for an employee list to make sure the contractor really has employees and won’t be hiring casual labor off the streets.
Ask for a copy of licenses.
Know what is covered by your insurance and what is covered by the contractors.