First of all, the car would be a 2010 Nissan 370z.
It would have a Veilside front and back bumper and side skirts.
Colored black with green Matrix code running from the front of the car to the sides and roof, fading out. Blacked out headlights, backlights, and grill with black and green Enkei EV5 Performance Series rims. Some awesomely custom rear spoiler as well. Oh, and a sun roof. Green tinted windows and slightly green headlights. ALSO..can't forget the underglow.
Greeennn. The interior would be lit with green LED lighting all around with green, black, and gunmetal grey bucket seats and a black dash. Standard shifting with a custom shift knob of sorts.
Now for the sound system.
A Sony Xplode system with Kicker speakers in cabin. In the trunk, there would be two 1500 watt Audiophonics amps bridged with two 15" Sony Xplode subs built into the base of the trunk.
And throw some NO2 tanks back there somewhere.
If I forgot anything, I'll edit.
I'll get to the engine later.