Matte Painting

I've been meaning to do this for a while but I'm finally getting round to it; I'm going to do a matte painting! I'm going to keep it pretty simple to start with. I'm going to take one of my photos from Japan and comp it into a simple scene and make it snowy! Below is the colour key I've done to work out the basic composition and lighting of the scene, and beneath that is the photo I'm taking as my starting point. I'll post my progress.