Pretty good so far.
The only thing I missed were some icons to preview the tile. Maybe if you select an item from the listview and a preview image appear above the add button?
Another thing was a clone/copy feature. Maybe holding the ctrl button while clicking on an already placed tile, it selects that tile from the listview and you can place it (without having to press add).
It was a bit odd to hold Alt and Middle Mouse Button to rotate the camera, it might be more convenient to rotate the camera using the right mouse button seeing as that button isn't in use in the 3d view.
Other than that, it was very easy to use, and building a small city, if you can call it that, doesn't take more than five minutes or so.
A mod accidentally your signature