Making a new level

Ok so i followed along with the making a map on 3d buzz but this time around i would like to make like a more urban map like a city or a neighbor hood How would i start that?

I think i would need assets like a ground and like building i can go into maybe?

Create a new scene (File>New Scene) for a new level. And for a city, with buildings, learn modelling- use sketchup mostly for that kinda stuff, but Blender is great too.