A format overview for a letter of request will be as follows:
The letter is left aligned. First, write your name and address details along with date.
Then write the name and details of the person to whom you would be writing the letter.
After leaving some space, start the letter with a salutation like Dear Sir/Madam etc.
The main body of the letter is divided into three parts/ paragraphs,The first paragraph states the purpose of the letter while the second lists relevant information and suggestions pertaining to the purpose stated.The ending paragraph is a conclusion of the topic on which you are writing the letter. End the letter with a courtesy like Yours Faithfully or Thanking You along with your name.
Hope it helps.