Hi,
This is not that uncommon. Neuonix was able to help me write mines. But then the prof changed his mind, and decided to write it himself. Be SURE to give the professor a LOT of information (your PS, AMCAS application, resume, transcripts), as well as what to write in a letter (if the professor is going to write it). I think my professor c hanged his mind once he saw all the background info i gave him.
It u sually start like.
I have known Jack Jones students for two years, including three quarters of Organic chemistry. Jack was a fabulous student, usually scoring in the top 5 percentile. Over the past 17 years of my teaching chemistry I have seen many premedical students, and Jack is clearly among the best.....
basically, how well he knew you, a brief qualification of himself as a writer, and how you did the class.
Well, that's the first paragraph. After that, i'm not too sure. I found looking in MSAR EXTREMELY helpful in deciding what to tell profs to include in the letter. the beginning of MSAR has a section on what qualities are important for a future physician. I copied those qualities down and told them discussing those aspects of my personality were important.
oh yeah.. i found this link when i was trying to decide how to write mines:
http://www.studentgroups.ucla.edu/ppa/sampleletter.htm