CHS Sizing for Shed

I need a structural engineer to confirm the minimum Circular Hollow Section that can safely replace the 150 PFC members shown in the attached shed drawings. The shed is in a C4 wind region, so your calculations must satisfy that loading scenario and comply with the relevant Australian Standards. I prefer a medium-wall CHS, but if your analysis shows a lighter or heavier wall is essential, let me know and justify the change.

What I will supply
• PDF plans and any dimensions you need
• Current member schedule showing every 150 PFC location

What I need back
• A concise calculation report (PDF)
• Your recommended CHS size (OD × wall) for each member replacing a 150 PFC

Need asap.