While watching the Olympics, I'd wondered why the Bird's Nest didn't have a retractable roof as it was raining down on the competitors and they were getting soaked.
Tonight, I finally got an answer while watching a National Geographic Megastructures show. The original plans did call for a less-open roof and a retractable roof. After the collapse in the Charles de Gaulle airport , construction on the Bird's Nest was suspended for five months while investigations took place. Apparently there were some similarities in construction between the two structures and no one wanted the same thing to happen again.
After the consultations, the design was changed and the retractable roof was scrapped. Now I know why the competitors were rained on. :)
From conception to construction, this was a unique, one-of-a-kind building. Even the steel they used was newly developed especially for the structure so that it would be strong and flexible, both able to withstand earthquakes and be flexible enough to bend and twist over the curves of the building. It's an amazing achievement. I think I'd like to see it someday.