Here is an example jobsheet that would be sent to a vendor to create a collection of assets that would make up an outfit that could be worn by a highly customizable male or female player character in combination with out clothing assets.  IIRC, I directed outsourcing for some 60+ outfits and 40+ hair pieces.

Higher level stylistic and technical guides were provided.  Many rules and templates had to be adhered to in order to make everything work.  Even then, our team spent a significant amount of time fixing problem combinations we missed in planning the setup.

My recommendation…avoid customization unless it is critical for your game.  It is very difficult, costly at runtime, and never results in characters that look as good as those that are created unique.  Still, it is fun for the player.