Ooh GCSE Graphics - Was my forté at GCSE :p
I would presume you're going to have to actually make a model of this, evidently not lifesize, I would suggest around 1:10 maybe to give around a 20cm Model. Now the 2D stuff could be a posted or instruction booklet to go with it, but that's simple and can be knocked up to a decent standard in a matter of hours.
To make your seat unique it will have to be stricking, yet simple. OTT things can look gastly. Keep the curves simple and flowing.
Needed:
It would need a place to connect a steering wheel, obviously ;) Optional detachable tray for the seperate gear changing unit from the G25 and similar products
[*]Surround Sound Speakers in head "rest"
[*]Research into Erganomics and Anthropometrics (how the human body would work with this, and also the individual lengths of the body parts so the average person can be "housed" in the chair) You should be tought a bit about this at some point.
Optional Things to improve aesthetics and function:
Blue neons (Flashing optional)! They always improve things, especially in the dark and are good for gaming geeks who stay up to the early hours! Flashing rate changes dependant on the sound - concept ideas don't have to work at GCSE or A Level ;)
[*]Mouse tray/plate in easy reach of arm (which can be rotated out of the way when not in-use) maybe to make navigation through menus easier
[*]Built-in controls in "arm rest" perhaps? Like real window controls or a "fake" radio with volume control perhaps
[*]Upgradable features, such as new seat cushions (that always gets you brownie points if you can think of the future)
[*]Make it "sustainable". Thinking of the environment is a plus in these sorts of projects
That's it for now, just standard stuff. The main thing which will make yours unique is the looks of it. The best ones out there cover all the essentials of the seat. If you make it looks clean, crisp and still make it confortable you'll be fine. The main bit with GCSE is the write up, if you manage to do decent drafts, evaluations etc etc then you'll be fine :) Although, saying that, if your final model is pants, you'll loose some marks.
You could base the design around the 911 Porsche Wheel which does work on the PS3 and PC. There are some ones which specialise in the G25, if you work on the Porsche one then it'd be unique :) Mainly as the final product has not been released yet. But there are plenty of Beta reviews on the net (YouTube for one) and pictures about.
Enjoy :D.