A couple things:
- The span on the support members to create a large open floor plan requires a large structural member to support that span. Hence the truss style frames
- The span is much larger than it looks due to drone footage and not actually being there in person
- The roof will have to carry some load: solar panels and heavy rain and wind
- The open sections of the truss will be used for infrastructure. Wires, ducting, even possibly equipment
Thanks for your informative reply! In the meantime I did a google search (which I should have started with...), and found this: Space frame - Wikipedia
To quote: "...a space frame or space structure (3D truss) is a rigid, lightweight, truss-like structure constructed from interlocking struts in a geometric pattern. Space frames can be used to span large areas with few interior supports. Like the truss, a space frame is strong because of the inherent rigidity of the triangle; flexing loads (bending moments) are transmitted as tension and compression loads along the length of each strut... With these features, steel space frames can be used to achieve also complex geometries with a structural weight lower than any other solution. The inner highly hyper-static system provides an increased resistance to damages caused by fire, explosions, shocks and earthquakes. Space frames are modular and made of highly industrialized elements designed with a remarkable dimensional accuracy and precise surface finish."
So, lighter, stronger, easier to manufacture roof solution. Cool!