OPENCART extension multi seller

We are currently looking for developer who can can create an OPENCART EXTENSION that will allow users to submit their own digital goods for example .pdf books for sale. We need an extension the same as in [login to view URL] website: seller acount (simple user can upload and sell his own goods like extensions in [login to view URL] ) * Every time when users sold their goods we will receive some percent (%) of commisions. * Sellers will be paid for their sold goods at the end of every month. Front end User section 1. User can create account witch allows to sell and buy from front page. 2. Users are able to manage their own goods (edit/add/delete) at anytime by simply login. Most probably to be shown at My Account page. 3. User can view a transaction list. 4. In user registration form must be a field about paypal contacts. 5. When user uploads a file he must fill their goods description. 6. When user uploads a file he must select a category from droplist. 7. Before uploading a file user must agree with terms and conditions. Admin section 1. Before a file will reach a sell section in page administrator need to check and approve uploadable file. 2. Administrator can manage all users files (edit/add/delete/change/change status). If you are uncertain of anything, please feel free to contact me. I will paste you more details. Please bid only if you are confident in doing it. do show us some demo if you have any related done project.