Right, she uses a 10" square madeira. Having done quite a few vehicles, I'd recommend freezing it before you start carving as it makes it much easier to take small slices off without it crumbling.
Level the top then cut the cake in half and place one on top of the other.
To shape the windscreen measure 3" from one end and cut down at an outward angle to about 1/2" above the bottom of the upper cake.
Trim both sides of the windscreen so it curves round gently then trim the front of the bonnet by rounding off the front.
Shape the sides and back by slicing down at a gentle outward angle.
Sandwich the cake together with jam/buttercream then spread a thin crumb coating over the whole thing.
Position on the board then thinly roll out a strip of black sugarpaste measuring 1" in height to go all round the bottom of the cake. Start at the back and unroll around the base, pressing in to place with a cake smoother.
Roll out white sugarpaste to 5mm thick and cover the whole cake, trimming away the bottom 3/4" so the black underneath is visible. Use a circle cutter to cut out the wheel arches and use a ruler and knife to mark the doors, windows, lights, etc.
Cut wheels out of thickly rolled black, using the same size cutter as you used for the wheel arches, indent the centre of each and paint silver for the hubcaps. Leave to dry so they don't flatten when you stick them on.
Dilute black colouring to make a very pale grey colour wash for the windows, darkening in places for reflection/shadow.
Paint the lights with silver on the front, cut out of very thinly rolled red for the back. Add bumpers on the front and back, stick wheels on, make wing mirrors out of black and stick on (might have to use wires to make them stay, ime).
Make door handles and windscreen wipers, and mark petrol cap with small circle cutter.
Vehicles are fiddly, you need to give yourself plenty of time. It helps to have a picture of what you're making (I usually just google and have it on the screen in front of me) so you can see where the doors, etc go in relation to everything else but they do look good!