Confirm the finished outside dimensions and mounting points.
Calculate cut lengths after allowing for the selected connectors.
Cut and deburr each profile before trial assembly.
Square the frame, add bracing where required and tighten fasteners evenly.
Test the completed structure with the expected load before use.
This project is a concept, not a certified engineering design. Adjust the dimensions, joints and bracing for the actual load and environment. Do not use PVC extrusion where failure could create a safety hazard.