The first & foremost thing is to know what you want. Any good cuemaker should be able to (within reason based on materials, etc) provide your requested...
Weight - within .1 to .2 oz
Balance point within 1/4".
Joint type & materials
Shaft taper, ferrule material, tip type.
These are - imho - the things that make a cue "feel good" in your hands when you swing it.
Hit & performance are elusively personal and dependent on a host of fine details in construction, material types & quality, and general application of "expertise".
Then you have to be realistic about how fast you want a cue in hand & how much you're willing to pay for it.
I can tell you from bitter experience that it's no fun to wait 1.5 to 2 years for a custom cue that, due to failure to appreciate the vast difference basic component choices can make in performance, you really can't play well with unless you're willing to learn to adjust all over again.
I play with the piloted 5/16-14 joint. There are many others, and I've tried lots of them, but I'm not willing to waste time & energy on the others anymore because I've found that this a basic component of where I'm comfortable.
I've only owned 1 True Custom, meaning it was made for me. mdavis I think says it well. I posted on Instructors asking about why I seem to play better with a cue that's feather light 15 or 16 oz. I've played for years with 18 and 19oz cues. A year ago I was handed a 14oz cue to try and it was a dream. Maybe a nightmare since I lost sleep thinking about how great it played.
Here's why I'm telling you this. Your job is to tell the maker exactly what you want. That's really hard to do if you haven't tried, like me, all the options and combinations of, Joint, balance, tip dia, shaft taper, butt dia, weight... If you have, you're ahead of the game.
I'd say pick a couple of reputable builders that generally has the look that you really like, then if at all possible, find some examples to try out. Write down what you've tried and or take a picture. Then when you find a couple that's close to what you want, call those guys and discuss what you like and don't like about it and see what they say.
With the cue I bought, it was sent to me semi finished with a variety of shaft tapers and was able to play for a couple of weeks, then we made decisions and adjustments. Don't know if that's a common practice but I'd think the maker wants you happy just as much as you want to be happy with the results.
Ask lots of questions. Some of these guys enjoy the challange of being as precise as their ability allows. This conversation is more than just talking cues, it's meeting the guy and seeing if you both want to work together on the project.
Finally, Go For It.
The process is great.