Don't you think it would be cool to rebuild Helgen? You could get some of your 'friends' in skyrim and they would help you to rebuild Helgen.
You saw at the beginning that Helgen had a lot of potential and it looked like the best village in the whole game.
What do you think? Wouldn't that be a great idea?
And this isn't a spoiler, because this happens at the beginning of the game.
Yh. This idea has come up a few times before and rightfully so. Its a great idea, so listen up Beth'

The other place which has been suggested is for Winterhold to be rebuilt into a thriving city. I think I steer more towards Winterhold to be rebuilt as it seems such a dull place. Winterhold has plenty of available land nearer the coast line and beneath the college and could do with a city wall. You can also get a horse cart ride there from all the other cities.
Maybe have the Dovahkiin (& hero of Skyrim) have a castle home built there. I'm sure having the Dovahkiin move there would bring people back to the city. That and now the Mages Guild has a new leader who also happens to be the hero of Skyrim