If you're going to use windows, as Rick suggested, you might want to consider using a 3D skybox and the City 17 skybox prop instead of images. Those images will look really flat on their own. Unless of course you want to build a couple blocks of London around MI6.
Also, I learned that Frexx had already made an MI6 map, but it was lost. There is a video though, maybe it will provide you with some inspiration.