Many builders are new to music, so here are some thoughts about what makes an instrument function better from a musical perspective.
Number of Strings and Tuning
There are endless possibilities to stringing and tuning a CBG. Using a standard guitar as a model is one choice. On a 3 string CBG using the 3 lowest strings (EAD) or on a 4 string CBG, the 4 highest strings (Dgbe) is one way to utilize standard chords and scales. Futhermore, it is possible to simply retune to an Open tuning and have another tuning to explore. EAD can be tuned down to DAD (the lower part of the full 6 string Open D Tuning - DADf#ad) and Dgbe can be tuned down to Dgbd (the higher part of the full 6 string Open G Tuning - DGDgbd).
CD 1 - On this CD I teach mainly 6 string played in Open D, but I also include 3 string CBG tuned DAD. I clearly explain how it is possible to micronize the 6 string down to a 3 string.
CD 4 & 6 - For 3 string CBG - Using strings ADg, I tune GDg (See note) This is the lower part of the full 6 string Open G tuning D(GDg)bd. On CD 6, I simply retune to ADf#. This is a part of the full 6 string Open D tuning D(ADf#)ad that makes possible a simple method of movable chords that functions very similar to the method used on a standard 6 string. "A great approach if you want to strum chords."
CD 5 - For 4 string CBG - Using strings Dgbe, I tune to Dgbd which is the higher part of the full 6 string Open G tuning DG(Dgbd).
By using this approach, CBGs and 6 string guitars are related. You basically are learning to play both. The different number of strings and how the strings are arranged offers various possibilities for arranging songs.
Note: DAD and GDg are fingered exactly the same. The difference is one sounds notes in the key of D and the other is in the key of G. DAD can be tuned lower to CGC/key of C or higher to EBE/key of E. GDg can be tuned lower to FCf/key of F or higher to AEa/key of A.