all of the roots are going to be exactly an octave away from one another every time. There are two important octaves to remember. One is two frets and two strings up from the original note, like the open low E and the E on the 2nd fret of the D string. The other is three strings up and three frets down, Like the G on the low E string, 3rd fret, and the open G string. The other octave is directly across the fretboard on the other E string. These miniature "shapes" are of course changed by one fret up every time there is an octave that goes across or onto the B string.

It is helpful to map out all of the octaves of a particular note across the entire fretboard as a visual aid. If you do, you will notice that it has a certain Kite-like shape, with a "diamond" and a "kite-string". If you memorize this pattern, you will never have any problem locating any roots anywhere on the guitar once you know where one is, because they will always adhere to this shape.