screenwall at roof level

I have a relatively tall screen wall at the roof level - about 20ft tall - around a mechanical area. The structure is kicked back into the roof diaphragm. What is the best way to model it so that RAM Frame accounts for its wind surface area? The footprint of the enclosure is much smaller than the footprint of the roof, so I don't think making my parapet taller is the right answer. 

Thank you,