I don't know why, but Sims 2 popped into my head and I remembered the tool that was supplied to make your own Sims.  The same was done in The Movies.

Will there be similar tools for making our own buildings?  How customizeable will the buildings be, ie. making skins to go over the meshes or making all new meshes AND skins, etc?

I recalled reading something about being able to customize a building's functionality to an extent in a review.  Is this correct?  If so, will there be an in-game wizard to help you with the process?  Will it have an offline counterpart that could be downloaded?