Write a website plan and navigation structure

Hi, I'm planning to setup an online mailing website. I want you to write a plan for it to help the developer. How this website works: If somebody wants to send a post and is far away from a postoffice or is busy, they log into our website, type a letter, pay for it and then we print, stamp an envelop and despatch the letter to its destination. One example of such a company is Ezgram.com. Find out few other successfull companies who do the same job and write me a plan comparing all these companies. Also find out who provides the cheapest service to send letters. Thanks