When designing a open structure c/c, you design the top of the roof structure and wall the normal way. The only thing you need to worry is the uplift pressure underneath the roof structure. This is outlined in ASCE 7.
Basically you make your best engineering judgment since it isn't in the code for C&C. You can also try other wind codes such as the British or Australian codes. I had a building department once suggest in their comments to use partially enclosed pressures. That seems excessive to me but would give you a number to work with and is in all likelihood conservative and therefore safe.
