Injury, burn, ... Sipping liquids too hot can cause a mild burn in the hard palate (roof of the mouth). Chewing on crunchy food can cause scrapes that also hurt. Certain viral illnesses can give blister on the roof of the mouth, but these are usually not isolated to just the roof of the mouth! Dental pain might sometimes be experienced as pain in the roof of the mouth, if you have an infected or injured tooth.
See dentist first. Check with your dentist first. Possibly, you have a burn from a hot beverage or food. Trauma is also a possibility. If the dentist feels that this should be evaluated by your MD, you will be referred.