I need to build a upload-download system similar to mediafire. Is there some customizable open source systems available, which i can download and cuztomize or I have to do it from start. What all things to be take care about. In my case atmost 500 MB of collective data have to be uploaded-Downloaded at once (Multiple Upload at once). Then the questions like "Server specifications to be used", "PHP settings like Max upload size, Execution time" etc arise.
Please guide me with the steps to develop a system in PHP-Mysql.