Build a Website

i have a website and i want you to build just the sign in system(both with google&Facebook) and the payment system with PayPal. details later. i need an experienced developer for this job. all users must have a PayPal account . the main work is on the payment system. the system will automatically add administration cost to the sellers product and separate it during checkout . the money will then be divided into 2 , one to the sellers account on PayPal and the order to administrators account on PayPal. both payment should be instant.