Remember that Open C, Open G, and Open D tunings all have the same string-to-string intervals, just shifted one string to the bass side respectively. Say you already know a chord shape that is a D (the V chord) in Open G. In Open C the same basic chord shape shifted one string to the treble will be a G (the V chord for C). In Open D, shift it one string to the bass for an A (the V chord for A). It's easy to find chords for Open G tuning. They're essentially the same as banjo chords. Just get a bluegrass banjo chord chart. I often play banjo tunes on guitar (in both Open G and Open C), especially if my wife has a headache.