sounds like something I've read also, but for the life of me I can't remember the title or the author (it was a good story though)
the plot though...
All the worlds land masses are covered by 'buildings'. The hero (?) starts out as the lowest of the low living in the dark under the buildings. He gets taken in and proves to be a genius, goes on to be hugely successful AND develops a means of traveling through time, or perhaps it was to parallel universes, i forget the detail. Finally he is contacted by himself from another dimension (pick one) and is given a crucial piece of information. In the end he dies, but his alternate self steps through and takes his place (nothing weird about that

). Story ends with all the buildings being torn down and people returning to live on the land...
does that sound familiar, or jog anyone's memory?