As I understand it (i.e. a total guess) the roof is designed to be more or less self-supporting due to its arch shape, when they first built the stadium the four steel roof supports seemed to go up (and stay up) independently of the specifics of the stand orientations. I'd guess that roof is...
Anything is possible with money, but nothing will happen without it. TB's already spend £100bn and we are only just about selling out 28,500 or whatever the current figure is. There is no money in it right now. We will be at 30,500 for a while yet I believe.