Don't mix too many different roof types when working with CD3. Try also to avoid the png buildings if possible. It is a good start for working with CD3 for the first time. I would like to see more CD3 maps here.

@Mark Oliva:
Most users use the predefined backgrounds, houses etc., because it is convenient I think. You can change everything, import textures for roofs and backgrounds and so on. In my opinion most people are scared when they see the UI of this program. Intuitive is a word that don't match with CC3.