In RWIND Simulation, you can specify the opening size in the "Edit Model" menu of the respective models.
The RFEM or RSTAB interface menu includes the opening size specification for the automatic calculation of wind loads in the background in the "Simulate and Generate Wind Loads" dialog box under the "Wind Load" tab.
In order to simulate a closed building structure, it is also possible to consider additional surfaces in the opening areas using an STL import, or directly, using a load distribution surface in RFEM.