If you want to start with an oil tank, as I said, be very careful and all that but OIL is relatively safe to cut. If it is FUEL OIL or GASOLINE, you should be doing something like piping exhaust into the tank before cutting or filling with an inert gas. I am only giving my opinion and in no way advocate starting with a used oil tank. You can buy a new one for roughly $375-450. It could be worth it to know it's never been filled.
Cooking for the love of it.