I use and have used a shed load of different CAD software packages the main ones are Catia, IDEAS, Solidworks. There isnt really a package where you start with blocks and add them to your model. You start with a blank sheet of paper - do your sketch then take it from there.
After the model has been created the computer model is then put in a rendering package such as Maya (Gran Turismo fame) or something like 3D Studio.
This is what I do for a living so if you need any help let me know.