Bespoke jeans are a luxury item. The luxury is wearing clothes that fit near-perfectly in an off-the-rack world. This level of craftmanship is a process of taking a dozen or so very precise measurements and delivering these numbers to someone in another state whose whole job is to achieve a miraculous end-state: a fully-satisfied, referral-giving customer. It is capitalism at its best!
Tips:
Realistically, perfection won't be achieved on the first try. You might be satisfied, but there will always be half-inches or more you wish you had added or subtracted. That's why buying two jeans on the first transaction is a smart move. They will be mailed to you one at a time and there will be an opportunity to final-adjust everything.
If you are buying just one pair, though, I strongly recommend that you recruit an assistant who has a good eye and is slick with that measuring tape. Measuring yourself solo is feasible but not ideal.
If you're a male, ask if men need to make any sort of anatomical adjustment for the rise. In my opinion, most men probably ought to follow the measurement directions and add a half-inch to an inch.
The only negative observation is that the whole process of placing your order through receiving your jeans in the mail takes weeks. If you have a time constraint, this might not be for you. But the fact that you visited this company's website indicates you like commissioning projects, building bridges, planning polar expeditions. This is the next-best thing.