Hey all, as has been said the blue building is in front of the pods, it looks in the perfect place for where the bbc tv studio is.
As for the cauldron, i watched the super structures tv program and some of the girders were actually unused metalic gas mains. I work in the gas industry and we use plastic these days which is why they no longer needed for gas. however i doubt they would be used. my bets is for the garden area across the canal near the barge, as it seems to serve no other purpose. that or something that fits into the big square hole on top of the orbit observation deck.