[pauljs75]

With Wings3D (box modeler), I find that it's easy to bulk out the shape of the car first and pull edges/vertices to match the print. Once the edges are in the right places to define the model, then I start cutting it up into pieces as necessary.

I've also seen people make models in the same program piece by piece and fitting it together. So it might be up to the modeler to find out what approach works best for them.

Also it depends on what you're planning to use the model for. High detail models are probably better to build by part (well if you're good at doing it that way) and low detail models are probably best made as one "brick".