It appears that the structure which collapsed while under construction was just one of a number of similar structures on the site. Many had been clad.
The most common reason for collapse of these rigid frame steel buildings while under construction is failure to install the bracing in the roof and longitudinal walls soon enough.
Early days, but it is difficult to say from the photos how much diagonal bracing was present. In fact, may be just my old eyes, but I can't see diagonal bracing going to ground in the completed buildings.
