diminished & augmented chords are the only practical chords whose notes are evenly spaced in the scale, the former separated by a minor 3rd, the later a major 3rd. therefore, the root of the chord in either case can be any note there-in. begin with any note. go up 3 half steps & play that note. repeat. repeat. another repeat brings you to the octave of your starting note. this is 1 of 3 distinct diminished chords being named for any note in the chord that makes sence in the context of the key of you're song. all of this applies to the augmented chord but go up 4 half steps instead of 3, there are 4 distinct chords, & you only repeat twice to get to the octave. you have forced me to use paragraph form. if you are still confused i shall resort to capital letters @ the start of every sentence & check my spelling.