What are your "must have" features when spec ing a custom
 

Id be interested to find out what are the features of a guitar that you must have when ordering, no matter who the luthier is? The stuff that you are not flexible on..

E.g. must have wood species, particular string spacing, armrest bevel, tonal characteristic.....whatever

String spacing, nut width and as musical a piece of wood as I can afford. After that, a trusting relationship with the builder. I used to be more fussy but then life proved me wrong.

With some builders and some styles of guitar, features like bevels may not be apt. Eg the traditional vintage type builds that seek to replicate the look and sound of the prewar martins.

If i were to commission a modern type build, I would favour adding the arm bevel if the budget can withstand it and if the builder offered that feature. I have gotten used to how the bevel on the sheppard that I used to own and now the ryan makes playing much more comfortable without the sharp edge of the guitar digging into ones arm.

A cutaway is nice to have but not essential for me - ymmv. I have not found the manzer wedge to make that much of a difference comfort wise for me.

Nowadays I am far less particular about what I would specify - i would generally want to order the model and the wood combination that the luthier is most confident and experienced in using to produce his desired results. I used to favour spruce over cedar but playing my ryan has changed my mind - it depends on the specific piece of wood and on the luthier.

I have found that I favour rosewood sounding tonewoods so I would probably only choose luthiers whose best combo involves some kind of rosewood sounding tonewoods.

must-haves
 

I am very specific about my wants when specing a guitar. In general, a body size that is not too small, nor huge, 13 or more frets, 1 3/4" nut, soundport, EVO frets, minimal but tasteful ornamentation. I go into great detail on the wood selection, which varies from guitar to guitar as do lesser wants.

After 4 commissions where I focused on every single aspect of the guitars, including cosmetic aspects such as bindings and rosettes etc, I've decided that the most important aspects are (1) nut width and (2) neck profile.

Nut width determines how much space I'll have when playing, especially fingerstyle. I like a minimum of 1' 3/4" but a little wider is even better.

Neck profile will determine comfort and ease of playing in my left hand. I like shallow modified V or low C for this purpose.

After those, I tend to like a vintage tone and beautiful though not necessarily fussy craftsmanship.

I am slightly surprised that nobody has mentioned the fretboard taper as an important parameter. This would be specified by stating at which fret you wanted the fretboard to be the same width as the string spacing at the saddle.

This is crucial if your playing style involves a lot of bending further up the fretboard.

1. The Sound. I have to believe the builder can produce the target voice I want that will have my ears melting in ecstasy. I'm driven to own a few of that small handful of the greatest guitars I've ever heard. I call them 'Exceptional' because they are the exception, not the rule, and are quite rare. My standards for The Sound are my own, of course, but I think I'm a pretty good judge of quality, and anything less than this won't hold my interest. All other build choices are in service to this goal and I usually follow my luthier's advice to get us there, including their recommended woods, body size, 12 or 14-fret neck, etc. If it's got The Sound, everything else is really a secondary consideration, but I usually also like a cutaway and a rounded V neck profile. All my guitars have necks based on a 1937 Martin.

There are always points in every build where I'm asked to choose between options that have no effect on The Sound, like do I prefer rosewood or ebony binding?, so I'll pick one, but The Sound is all that really matters to me. As long as it has that, I can make everything else work, and if it doesn't have it, I'll move the guitar and try again with someone else.

It's the quest for Excalibur, and if you're persistent, and know The Sound when you hear it, you might find a few in a lifetime of playing.

1 13/16 nut - 2 5/16 saddle spacing - sound port(s) - lightly built - wood bindings - and a little bling to make it "mine";)

When I commission a guitar the first thing I do is determine how I'm planning on using it and what I'd like to hear from it. Is it replacing a guitar that I tend to use for certain styles of music and styles of playing, or is it a guitar that is filling a 'void' for a certain style/tone? I also define how I will be holding the guitar, and where I'll be playing it. Based on these decisions I try to define the aspects of tone and playability that will contribute to what I want.

The "must have" features that I want on every commission would be:
Responsive enough for fingerstyle playing without picks.
Spacing at nut and saddle, along with fretboard radius/width and neck contour, that works for my fingerstyle playing.
Sound port.
An aesthetic that interests me and gives me something to appreciate each time I pick up the guitar.
A guitar that does not compromise in what I want for tone, playability, and aesthetic.
A guitar that provides a good value, however I'm defining that at the time.
A builder I'm comfortable with and whom I respect for their knowledge, skill, and method of doing business.

Low action and electronics are the must haves.

Wider string spacing is nice.

I enjoy a bevel, but it's not a huge requirement unless top to back depth is big.

Definitely will echo nut width, string spacing and neck shape (I don't know how or why people play necks with hard V's or overly thick) And must be responsive to a light touch.