To make it look like one you'll need, the wheels & possibly spacers, both bumpers, sideskirts, front wings, grilles & the badges. You'll also need the interior too (all seats, steering wheel etc) Plus probably some other bits i've missed off.
Once you've done all that you'll still have a car with a sunroof, 172's etc don't have them, so that would be a giveaway.
All in all unless you can get all of the parts cheap I really woudn't bother atall.