It all comes down to 2 things: material and assembly. You want stainless steel, anodized aluminum, high durability plastic, etc for most of the construction; high quality pleather, velour, or well-treated leather with good foam for padding and ear-cushions; non-degrading polymers and glues for the diaphragm and driver assembly. Also metal screws in place of glue or heatbound plastic joints where possible. In terms of assembly, you want as little discrete pieces as possible in design, with everything fitting together like a jigsaw with minimal stress on any part or joint when fully assembled. All while trying to have maximum sound quality.