LEGO building, like most artistic endeavours, is a skill that one generally builds by imitating what other people have done, and for most LEGO fans the first master they study is the LEGO Company itself. Most MOCing techniques in a budding builder are based on what he's been taught to use in a LEGO set and when a builder steps out for the first time to build a MOC, the results are often close to official sets.
While I would like to think that I'm a bit beyond simple imitation of what goes on in official sets, I still do the occasional "paint job." I'm calling it that because the finished product is an official set, but painted with different-coloured pieces. This car is the most recent example:
Like a lot of paint jobs, this revisited car is a smaller vehicle. I tend to enjoy this scale because the smaller size makes it easier to find the pieces required in another colour to replicate the original. It's also a scale that LEGO does well. With most buildings they either have to skimp on parts or on size to keep the set's piece-count down to a manageable level, but this is not generally the case with vehicles.
The main reason for repainting this police car as a fire chief's car was the fact that I had the red 3x4 slope with wheel-wells and it even had the fire sticker on it, a relic from 6525 Blaze Commander, one of my earliest Town sets. I also had a spare 4x6x2 sloped cockpit. Between the desire to put both these parts to use and having more wheels and tires than I'll EVER use (true of most LEGO fans), this car fell together without much difficulty. It helps that it doesn't require any rare pieces.