I agree with bbradk....
Don't build anything there. Make it a true memorial site. Trees, fountains, statues, parklike. Fitting in my eyes.
I also agree with Veni vidi vici. From an architectural point of view the towers were rather uninspiring. Just a box.
BUT from an engineering point of view, they were incredible. To build a structure, nay, to build two structures so incredibly tall that stood proud against everything nature could hurl at them.
There was a documentary on TLC recently, something like, "anatomy of collapse". They interviewed the structural engineer who designed the towers.
He is a very unassuming guy. They interviewed him in his office, he answered questions put to him as opposed to taking the fifth. Quiet intelligence, you can just sense it. You can also sense how he is in agony over what happened. The poor guy, without saying it, is blaming himself. I wish i could tell him that nothing could be further from the truth.
It pained me to listen to these idiots rip apart his design when they wouldn't have a clue how to build a log cabin even. There is no way in hell that he could have forseen what happened. I am not so sure that a building of that height could be designed to withstand a similar situation.
The one thing i never ever understood though is why they don't have boxes of parachutes on the roofes of such high buildings. IN the case of the WTC, hundreds of people ran UP because they couldn't run down. If there were parachutes on the roof, I would sure as hell take a shot at it. I have rolled this one around in my head, and i can't see why it wouldn't work.
Stunt men jump off tall buildings with parachutes, if my back was to the wall, i would too.
Just a thought.