The architecture featured in the game...
...was partly inspired by these real rooftops,
in the fine city of Cardiff.

If you ever happen to find yourself in the Marriot hotel,
in a room facing the city, glance out of the window, and there's
de_rooftop in the flesh!

(If I ever come across the sketch I made again, I'll post that here, too.)

(click on images for a closer look)