The simple way to do it would be to keyframe the letter/chalk animation (there is a 2.5D move when they swing around to start writing) in the beginning, then use a write on effect to reveal the outlines (which you've masked previously), then masks to reveal the building details you've already made in photoshop, animated solids for the spotlights, and a camera move to "crane" up to the logo above the city. That's a basic way to do it...
The first part they just drew the building with the pen tool. Then with that pen like figure, the connected it to the beginning of the mask, added a stroke to the layer, and moved the pen from point a to point b, with it following the mask they drew.
the shading and such is with a stroke effect, but its neat and involves a little more work.