I don't worry about build quality much because you never know how good the build quality of your particular headphone used in your specific environment is until it actually breaks. For example, some have issues with RE0 falling apart after only a month or two of use, or even defective out of the box, but others have already used it for a year or more with no problems. Or take SE530 - the cable on mine hardened after two months of use, while I know some people who have owned the IEM for over a year or two with no problems at all. In other words, build quality varies not only from model to model, but from unit to unit, depending not only on quality control at the factory, but also on how extensively it is used, how it is treated, the user's environment, etc, so you just never know how durable a headphone will be until you actually use it and see for yourself.
I care far more about sound quality, fit and ergonomics.