Tweaking
What I felt was lacking from the image at this point, was a bit of bounce light to illuminate the doors and windows. This will add more detail to the image and make the image a lot more interesting. I could add bounce light in the Mental Ray renderer but I wanted a bit more control and to be a bit more artistic with the bounce light rather than leaving it to be mathematically correct. I started with the doors on the left. I added a low intensity MR-Omni Area light with a small attenuation to only affect the nearby geometry. I removed shadows cast so I didn't get any unwanted lighting issues.
Here is an image of the settings used for the bounce light (Fig.23).

Fig.23
With the tweaking completed, it was time for a medium settings render so I could see if there were any errors that needed fixing before taking the plunge and setting up a final settings render.
Medium Render
I set the renderer to medium image precision and medium Final Gather settings. At this point, I still hadn't enabled bounce light as it would have dramatically increased the render times. With the new settings I was able to see any problems that may occur.
Here are the settings for the render (Fig.24).
I was quite happy with the medium render and I couldn't see any major issues. Some colour correction needed to be done in Photoshop but this is normal with any image; it adds that extra bit of polish to the image.
I was now ready to go ahead and set up a high quality render.
Final render setup
The render times for the final render will be quite long, so be prepared to not be able to use your computer for a day depending on how good your PC is.
Here are the settings I used to get the final render (Fig.25).