Starting with a part built Tamiya kit that I found on ebay. I'm already in the process of replacing the plastic upper hull with a homemade aluminium one. I cut up the plastic hull into panels to use as a template to make the aluminium panels. I then positioned the new cut panels on the tank chassis and tacked them together with epoxy putty.
As you can see, I also integrated parts of the plastic panels where there is detailing.