Here's the initial rough sketch. The building is actually a take on the Brunel University Lecture Centre (http://www.movie-locations.com/movies/c/AClockworkOrange_BrunelUniversity.gif).

After quickly wireframing & planning from the sketch, I got busy gathering images of clouds. The sky is the only part of the image I did not fully paint myself.

Here's the finished sky.

I started with the landscape, the mountain range at the very back. I wanted to build up layers from back to front.

Here's the second layer I added.

Here's the foremost mountain.

I then added the range on the left.

I added greenery to both the left mountain, and the foot of the right foremost mountain.

I then played around with some adjustment layers, to get the seperate parts' colour & contrast right.

I introduced a bit of distance to the image, and added some smoke/mist.

Here's the overhang. I played around with proportions a bit before settling.

It looked pretty lonely as it was, so I put in a rock formation at the foot of the cliff.

I then added a waterfall - pretty pleased with how it turned out!

The building was more difficult; I had to seperately draw each part and shade accordingly.

It worked out fine though. After adding some texture (The weathered look, neon lights, '44' etc.) & adjusting it a little, it came out looking pretty dystopian.

I adjusted colour & contrast a little more.

I then drew the ship/flying thing, and added spotlights to the building.

Finally, after playing around a little more with adjustment layers, lighting & adding some sort of bubble shield to the building... I had completed the image to my satisfacion.