Dear Friend, your question I believe is self supported or supported roof. You are clear you need a fixed roof. So to add to your clarity, it can easily be self-supported cone roof tank. But as some members pointed out, I would like to clearly indicate, check if you are storing crude palm oil or fatty acid oil, then probably you may look at supported cone roof, but more than this, better check your shell thicknesses, for such products, as I have some bitter experiences for these.