Letter of introduction

I need some help with writing a letter to a girl's father. The intent of the letter is to introduce my self and also to ask him for permission to start dating his daughter. I do not even know what to include in the letter nor how long it should be. A written letter is the only meathod that I can use to get in contact with him. I also wanted to make it clear to whoever reads this that I have never met him which could also be inferred from that previous text. Any help I could recieve from those of you who could help would be greatly appreciated.