Hi,

How should i know the selected shape for the rafters when i collect the roof type as Cone or Supported Cone?

thank you,

A "Cone" roof won't have rafters.

A "rafter supported cone roof", and a "Supported Cone roof" both have rafters. Based on the size of the tank you should have an idea as to what cross-section will work (there could be other reasons also to choose a particular cross-section, like availability). This is why the user must specify this information to the software.