The Stainless Steel or Wood Cabinet Cage Builders are the only ones that are still likely building custom cages. Custom cages have they're benefits, but they have near zero resale value, i.e. at or less than standard used cages, which is tiny compared to purchase prices. If you can find one, you will need deep pockets and be willing to wait until they cage is build and shipped to you.
Are you sure that you really need a custom cage? If you are doing this for decor, what happens if you want to move the cage or change styles?
So, if this is still something that you want to do; web search the above likely sources.
I have a few of the Hybrid cages from Cages by Design, and I've been very happy with them. I also know some folks who have custom cages from Expandable Habitats and Northwest Cages, both of which appear to be excellent quality. None of them are inexpensive, but not unresonable when you consider that they will be a lifetime home for an animal that can live for decades.