Hi Keith - My personal way is a combination of both. Build a single solid if possible and then separate it into joined surfaces or single ones if needs be, then it is easier to map it out. However, after saying this, you should also consider the materials to be used at render time, so as an example, shiny or dull metals don't really need uv mapping and can usually be handled by procedural shaders, as can glass and plastic etc, even those that require bump mapping via noise or fractal maps.

Martin
(TpwUK)