Roofers have been targeting residents offering external property maintenance such as fascia and guttering works via a flyer or local advertisement posted through their door. Such literature may give an address that is not genuine, only give a mobile number, and often can indicate 'special rates for OAP's' to attract business. Please be wary. Check validity if they are claiming to be a member of any trade association.
Best advice would be to always use local, known traders that you have a landline and legitimate address for. Ask family and friends for recommendations. Remember, if you agree to a contract in your own home you will have 14 days cancellation rights, 14 days to change your mind.