Custom rifles or customized rifles can be done my many competent gunmiths, some like me specialize in the more tactical style bolt action rifles and long range hunters.
The key to finding the right guy for the job is to figure out exactly what you want the rifle to be used for, and what features fit your bill.
The next part is to satify in your mind that the person you select understands the needs and that you are comfortable dealing with them.
There are some fellows in the trade that either will agree to everything in an instant, they may be hungry and need your $$ more than looking to fill your best interests, or try to talk you away from something with no real grounds , if there is solid reasoning behind the objections fine, some things do work and others do not. Doing some research as to what a smith has real expertice in will help you decide as well.
For example, I can make pretty fair tactical rifles, and long range hunters, I also do some ultralite builds, but my main focus is bolt guns, I am not tooled or knowledgeable in falling blocks . levers, or non military semi autos, it just is not my interest, so I specialize in what does peek my interest. Others in the area have a well known following for their abilities with levers and so on. There are many different custom makers in all of the types of rifles, so my advice is to shop around for someone who can put together what fits your needs and wants.