1. Design a sedan.

The classic way to make a coupe

2. Cut the sedan design: remove the 'B' pillar, remove the rear door, shorten the wheelbase some, add rear side glass...

The classic way to make a coupe

Coupé:

From the French language, past tense of the verb 'couper', "to cut". More on the coupé body style on Wikipedia (makes for an interesting read).

3. Adjust the design a bit as necessary, don't worry too much about rear passengers.

The classic way to make a coupe

And voilà, you have a coupé.

Drawings by Yours Truly ( www.pgcomics.com).