Ok, so I've modeled a car (VAZ 2107), but when I was modeling I did just one side of the car to save time, and because it is easier to model and texture interior that way, and I thought I could mirror it, but when I mirror it, it looks as though rotations of the model did not mirror, and it looks like a mess. Someone please help to solve this problem.
It's not a bad start to the model, i'd like to see it finished.
Back to your question, modelling like this CAN work, it's just that while building the model you would have to make sure that every single part is on the same offset point, then when you mirror the parts they will all mirror around the same point, making the model look correct.
It won't work with your model anymore, this one will have to be finished manually, but keep in mind what i said for the next one and it should work your way!