What is a real good 2d3d cad program to building star trek ship's?

i am looking for a real free program that will help me build star trek ships in 2d3d.i have look in cnet.com& look in google.com but no luck.what i need is a cad program that is really for free.plese help me out .dont just tell me to go to a web site that does not help me or does not have what i truelee need.some people will tell you to do here and it will not help .