MDL --
I have had two custom tenor ukes built for me, and in both cases, the process and product were delightful. The luthiers sent pictures and updates, and they asked questions about details not covered in the original specs -- did I want a sound port, string choices, inlay? all like that.
In the first build, the luthier's list was short -- because he's got a daytime job, he's doin' all right -- and he limits his number of customers. Because of this, the schedule was but four months. Looks great, sounds great, plays great.
The second build, the luthier is an up-and-coming young fellow whose list has gotten longer pretty fast as more people have noticed him. I had a choice of woods, of which I saw pictures, and he has a special page on Facebook for his customers upon which he posts in-progress pictures, as well as images of his cat ... Looks great sounds great, plays great. (The uke, not the cat.)
In both cases, I did as much research as I could online. Found websites, read reviews, watched videos, and emailed some owners to asked for their input. Started email dialogs with the builders and listened to what they had to say.
Probably the best advertising is a satisfied customer, and a builder with a good reputation for delivery, art, and craft is apt to be a better bet than one with a pile of gripes. Maybe not, but that's what called to me.
If you are dealing with a one-person shop, there is probably going to be less certainty for hard delivery dates than from a place where there are several people building. Coming from classical guitars, where the fastest delivery can start at a year or two and run much longer, most of the ukulele makers seem to be quicker.
Murphy's Law will tell you that stuff can go wrong, and you can't predict the weather too far in advance, but if you find a place where the customers came out happy and are still happy after they have had a chance to play their customs? Odds are in your favor ...
Um. Forgot to put their names in, sorry: Michael Zuch and Beau Hannam, respectively.