classic motorcycle forum

Hi i found a bsa fuel tank in my late grandfathers garage. I do not know much about this except for it is rectangular shape with a curved back, green in colour and has bsa bicycles birmingham on both sides. It is in need of restoration but i really do not know what to do with it or how much it is worth. So if any one can help me or is interested please let me know as it will be much appreciated.  Many thanks jamie.