In today's economy how do you know that the "roofer" you choose is Professional, Licensed, Insured and honest? With so many so called "contractors" it is up to you the consumer to do you're homework on a contractor before you hire them. You should never take the "contractors" word or written word to be true.
You need to first verify their license and you can do that by going to The Department of Business & Professional Regulation. Only State Certified Roofing Contractors can Replace a roof or perform roof repairs. General Contractors and Builders are only allowed to install a new roof on a new residence or Building that has shingles or wood shingles. They cannot install any type of Low-Sloped or Flat roofing systems or cannot replace a roof (reroof). Some companies are not State Certified but hold a Residential Roofing License that was issued by a certain county and they can only perform roofing replacement or repairs in the county in which they are licensed!
Then you should check on their insurance status by requesting a certificate for Worker's Compensation and Liability Insurance. Do no take the certificate as being true. You need to call the insurance company not the insurance agent to verify that the insurance is in force and the premiums are paid. You can visit the Florida Department of Financial Services they regulate Worker's Compensation insurance.
Once you have verified they are legitimate then you should check the Florida Roofing, Sheet Metal Contractors Association (FRSA) and the local roofing association North Central Florida Roofing & Sheet Metal Association (NCFRSA) and see if they are a member.
Once you are comfortable with the contractor you should never give more than 10% as a down payment. If some asks for more then they may not have the capital or credit to get the materials to complete your job.
Once your job is complete you should ask for a passed permit (county or city inspection) and most of all a final release of lien from the contractor and the materials supplier who supplied the materials for your roof. If the contractor does not pay the materials supplier then the materials supplier will place a lien on your home and you will PAY TWICE for the same materials!