Cigar Box Guitars Have Soul - The look and sound of every CBG is unique and as different as the people playing them. So what may work great for me may not be the best fit for you. 
Here are some basics that may be helpful in finding your perfect CBG. 

Scale Size Matters - I have seen 5 year old children playing huge classical guitars like pros. So it is possible to adjust to the size and fret spacing of any guitar, but why should you? As a person with smaller hands I have always struggled with standard 6 string guitars. The frets are far apart and I have a hard time reaching. The scale of a guitar is the distance between the nut up by the head or tuners and the bridge usually located on top of the box that the strings go over or attach to. The longer the scale the further apart the frets are from each other. Many people have tried to play guitars in the past only to get frustrated because of the difficulty in reaching the right spots on the fret board.  
On a typical store bought guitar this scale length is usually between 24 3/4 to 25 1/2 or somewhere in-between. This is kind of a standard developed by Gibson, Martin and Fender and is ok for most folks with normal to large hands. But what about a youth player, lady or someone with smaller hands. Or those who play mandolin or ukulele? 
A shorter scale is one of the advantages that can be realized when purchasing a custom built instrument and can be the difference between struggling and easy to play. Even those big giant dudes that ride big motorcycles or big mud trucks will notice how easy a shorter scale can be to play. 
A shorter scale may be for you, so consider the scale when buying a CBG. I have found a 20" to 22" scale to be just perfect for most small hands players. 

Frets or No Frets? - CBG's can be purchased with or without frets. Frets are the narrow metal pieces on the neck that your fingers push your strings down on. 
Most common store bought guitars have frets but you don't have to have them to be able to get the individual notes you want out of the strings. Take the violin and chello for instance, these are examples of fret-less stringed instruments. 
There are advantages and disadvantages to both that can be considered and this topic alone can bring up much debate depending on who you ask. However there has always been something of a general rule regarding fretted or fretless. If you want to play primarily individual notes as in the lead of a song go with frets. If you want to use a slide go fretless. In my humble opinion, if the neck of a CBG is built well you can do both with either. So there is no right or wrong answer here. If you are used to frets buy a CBG with frets. If you have no preference, fretless may be a good option for your first CBG because they are usually less expensive. Typically the luthier has less time in the assembly of a fretless instrument. A good fret job takes some time and must be done right.

Action or String Height - The action of a guitar refers to the distance between the bottom of the strings and the frets or neck. A stringed instruments action or string height determines how much downward pressure must be applied to the strings in order to make solid contact with the fret or fret board. Like the decision for frets or fretless there are players that like both. Here are a couple of considerations regarding whether a low or high action may be best for you. 
If you have strong calloused fingers the action will not be as critical for you. If you are a new player, you can look forward to developing those much needed finger muscles and callouses and, you would want the action to be as low as possible starting out. Typically a guitar set up for slide play tends to be just a bit higher and this is normally what you see with fretless instruments. I have always been one to try and get the action as low as possible. The straightness of the neck and the fret job determines how low you can get the action on any guitar. If the action gets to low the strings can rattle on the frets. This is called fret buzz and its not a good thing. Fret buzz can also happen if the neck has a bend or twist, or if the frets are not correct. If you desire a low action you may want to look closely at the construction of the guitars neck. Hardwoods or necks made of 2 pieces (neck & fretboard) glued together are usually stronger and straighter possibly allowing for a lower action setting.

How Many Strings ? - Cigar box guitars are available with any number of strings from only one to six or even more. 
Certainly there are no rules, however the most common are the 3 and 4 string CBG's.
If you currently play a 6 string you may consider the 4 string. It may also be a good choice for the mandolin or ukulele player as well because it can be tuned and played the same. Both 3 and 4 string CBG's are well represented on YouTube with help-full teaching videos and this is a great resource. 
With exception to the above folks, I would recommend the 3 string to everyone because of the great sound you can achieve and the way it can be tuned making it easy to learn. There are many different ways to tune a guitar. The most common tuning for CBG's is open chord tuning.  Strumming all 3 strings makes a chord without pushing any down or in the open position. Depending on the size of the strings you can tune it to any chord you like, allowing you to play in different keys. 
3 strings will allow you to combine 3 separate notes to make a chord. The more notes you include in a chord the better it will sound. While many chords really need more than 3 notes, you can learn tricks to cheat just enough with 3 strings to make it work. So a 3 string is an all-around great choice.

Well there you have it! It’s all just my opinion and what I try to convey to the folks who have chosen to play one of the CBG’s I built. Hope it helps.