Only music majors and massachists like to re-invent the wheel by trying to build these things on their own.
Music is a language that has rules, mathmatical rules.
There is so much math involved in the creation of music that a few music savvy programmers have made web sites that can show you a new scale, or build a chord for you. Here are a few links to help you build chords and scales. It has a neat fretboard display that automatically updates when you build a new chord. This is a great learning tool for keyboard players everywhere. Now bass players can create a scale based on a root note, mode, and other stuff.