Ask to see their license.
You? Your employees? Are you subcontracting the work? If so is that company insured? How much experience and training do they have?
Ask to see their liability and workers comp. certificate.
Ask for several, call them, look at their work.
Design features? How big should it be? How many levels? What will the railing look like? How will the bench be built? What direction will the deck boards run
What kind of material should be used and why? 2×4 or 2×6 decking? Do you provide visquene and stone? How thick and what color is visquene? How large is the stone?
What size post, beam, and joist do you use? How do you secure your beam to the post? How will you bond or attach the deck to the house? Would you recommend a “skirt” around the deck? Who will call MISS-DIG? If you hit an electrical, gas, telephone, or sprinkler line who is responsible? How far apart will the deck boards be and will any be spliced?
Who is responsible? When will it be done? Does the left over material belong to me?
Will you apply for the permit? Is this included in the price? Who will get Homeowners Association approval?
How long will the job take?
How much do you want at the start of the job? Do you expect payment instantly upon completion?
How long is it in effect and specifically what things are covered?
Do you provide one? If your builder does not pay his supplier, the supplier can put a lien on your house and sue you for payment.