i got to do a matte painting for the photoshop classes but i really dont know what to do.

The image I'm working with :
http://img40.imageshack.us/img40/2568/imagedpart.jpg

The result so far :
http://img229.imageshack.us/img229/5024/midrender.jpg

ps:My images are too big to be posted.

Any idea of what i could add?