What is your license number?
Then check it while they are standing there. This is the whole point of a public register.
How long have you held it?
Tenure is public and it is on every listing here. Some Minnesota firms have held a license since the early 1990s, and that is worth knowing.
Who is actually doing the work?
The licensed business and the crew on your roof are not always the same people. Ask, and ask whether subcontractors carry their own credentials.
What permits does this job need?
A contractor who works in your city routinely will know. If the answer is vague, your city's building department will tell you for free.
This is a directory, not a law firm. Nothing here is legal advice, and where the honest answer is “ask your city”, that is what it says.
Where this comes from
The department's copy is the live one. Ours is a dated snapshot, and the date is in the footer.