I think that the US [b]should[/b] finance the reconstruction. $1.2B is cheap for the prime piece of land that the UN complex occupies. So, I propose that the US float the loan, on the condition that the complex is offered as collateral. Miss one payment and the buildings are ours. Evict the tenant and rent the space out as offices and apartments. I don't know how much potential rentable square footage the UN building has, but at $125/rsf/yr, it shouldn't take too long to recoup the $600M interest.
Trouble is, though, that the US hasn't got the [i]cajones[/i] to stand up to the UN. Never has, never will.
What do they need a HQ building for anyway? They should be having meetings at the Holiday Inn. Hell, the management staff at the last few motels I've been in look like the UN anyway.