Would think that you would be better off with a fixed roof for either of these fluid services. A fixed roof tank will be less expensive. Floating roof tanks are broadly divided into internal (IFR) and external (EFR) floating roof tanks. IFR tanks are used for liquids with low flashpoints (e.g. gasoline, ethanol, etc.).
Do you mean a self-supporting cone or dome versus a structurally supported cone?
If so, the difference is partly owner preference (for corrosion concerns, etc.), partly design (steeper roofs work better with pressure) and mainly economic (whichever can be built cheaper in a given case). That last item would vary from situation to situation, and would depend on your erection equipment, labor costs, and other details.
We can take thumb rule as if tank ID is less than or equal to 8 meters then go for Self supporting roof tank and if tank ID is more than 8 meters then consider fixed roof tank
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.