I posted this quite a while ago. It does not show how to make the final tank. I show how you can create patterns and make sure of the size and shape before cutting metal. viewtopic.php?f=3&t=5442&p=54797#p54797
I made mine out of wood. first made a cardboard template then cut and shaped three pieces of 5/4" cedar boards. glued them up so that the top of the outer boards will be flush with the top tube on the bike.