Complex sentence: The builder has to paint and assembled the model, preferably with an airbrush however they can also be painted with a regular brush using a variety of techniques to achieve similar effects as when painting with a conventional airbrush.
Split into simpler sentences: The builder has to paint and assembled the model, preferably with an airbrush. However, they can also be painted with a regular brush using a variety of techniques to achieve similar effects as when painting with a conventional airbrush.