Nah, put the CIA and FBI offices on the top floors. And on each floor put a plaque with a list of the names of the dead from that floor on it.
I was thinking, if instead of two towers they made one tower with a base so large it covered the area of the base of both the original towers, would a similar attack wipe out a whole floor, or would it leave part of the impacted floor intact enough to allow those above to escape?
I don't know...you're talking about a lot of momentum, and a lot of energy released in such an impact. Theoretically I suppose it would be possible. I'll have to ask my roommate (he's a civil engineer).