I would start with a sheet of paper and a pencil and draw some quick and rough sketches before turning to the computer.
But before you should read through the current regulations (2014
http://www.fia.com/sites/default/files/ ... 1-23_0.pdf
2015
http://www.fia.com/sites/default/files/ ... -06-29.pdf) on bodywork, the survival cell and crash structures.
Do you know what the reference plane, the front wheel center line, the cockpit entry template, the section AA, BB and CC is?
If not google or simply read through scarbs's blog
http://scarbsf1.com/ where a lot of these things is explained.
Dear FIA, if you read this, please pm me for a redesign of the Technical Regulations to avoid finger nose shapes for 2016! :-)