What notes are in a Gsus4 chord?
= G, C, D, (F)


That would certainly be technically correct, muso, but fairly difficult to achieve in pure form. I suppose it's always an issue [a delightful one, mind ] that playing the same notes simultaneously on 2 or more strings of a guitar isn't equivalent to playing the note on one string. The chord takes on a drone, a different flavour, and different compatibilities with other chords (and shades thereof). As such most chord-shapes are trade-offs, even the beginner's "standards".

The sort of shapes I'd use for Gsus4 would be:

6th String 3rd fret (G)
5th String 2nd Fret (B)
4th & 3rd Strings open (D & G)
2nd String 1st Fret (C) * only difference from a basic G
1st String 3rd Fret (G)

or -
6th String 3rd fret (G)
5th String open (A)
4th String 2nd Fret (E)
3rd String open (G)
2nd String 1st Fret (C)
1st String 3rd Fret (G)
- to go more in an Am7/C direction.
Then take your finger off the 6th String (making an E) and move it down to the 5th string 3rd Fret (making another C) and - hey presto! - you have a C (add G) shape.

You can also make a totally different Gsus4 by doing an Esus4 shape (3rd, 4th & 5th strings 2nd fret, rest open) barred on the 3rd fret. That makes the notes
G,D,G,C,D,G - closer to a pure version.

You may gather that I just love the "shadiness" or "merginess" of guitar.

For any guitarists out there, here's my favourite recent discovery. It's a luvverly Am shape (I think Am7+9 ish) that stretches your fingers a bit, but worth the effort!

6th String open (E)
5th String open (A)
4th String 2nd Fret (E) [2nd finger]
3rd String 4th Fret (B) [4th finger *this is the stre-etch]
2nd String 1st Fret (C) [1st finger]
1st String 3rd Fret (G) [3rd finger]

Works brilliantly with the Eurythmics' Here Comes The Rain Again...