Today I have cut out the whole for the 120mm fan at the top of the case. I went and bought some cutting discs for my dremel. I haven't cut metal before so it was quite an experience with all the sparks flying. I ended up using 2 discs to cut the circle. The first disc broke in about 2 seconds but the disc I used after that was a reinforced disc which managed to finish the job although it is quite worn down.
I also drilled holes for the top panel and fixed the panel with brass dome head screws which I think match the colour of the case.