Answer:
In RFEM, you can define various types of orthotropic surfaces. The information about the calculation of respective coefficients of the stiffness matrix is available in the Stiffness Matrix tab by clicking the [Info] button (see the image).
The self-weight determination is based on the specific weight of the material as well as the values defined in the windows of the selected orthotropy type. To consider the self-weight, there are separate text boxes available where you can enter the equivalent plate thickness, for example.