Most fishkeeping hobbyists have standard aquariums - glass or acrylic tanks that are mass produced in standard sizes (e.g., 10, 20, 55, 75 gallons). The reason for this is availability. You can purchase these tanks at your big box pet stores (e.g., PetSmart, Petco, Pet Valu, Pet Supplies Plus), independent LFSs, Wal-Mart, etc. On the other hand, some fishkeepers have custom aquariums.
Why would cichlid hobbyists want custom made tanks? Some cichlidophiles have tanks built for specific display locations in homes (e.g, in walls, furniture), some have them built for keeping or breeding specific species, and others have them designed for a unique look. Whatever the reason, there are vendors that will build that special tank for you. Below is a video from Custom Aquariums out of Wisconsin.
Video of fish tank fabrication at Custom Aquariums.
The downside, of course, is cost. A custom tank is more than just a few pieces of glass or acrylic siliconed together to create unique volumes. The more customized the tank, the more expensive it becomes compared to the mass produced standard versions because the process becomes less automated as customizations increase. For example, the components are cut to size based on your specifications, and then the assembly process is modified to accommodate your other choices. Many parts of the fabrication workflow may be modified just to construct your individual tank - whether it's a shallow, rectangular version or a tall, hexagonal design. Options include glass/acrylic thickness, glass clarity, joint types, tempering options, rimmed/rimless, pre-drilled, and of course volume and dimensions. On the other hand, depending on your options, you may well find a vendor who will construct a tank of the exact same dimensions for less than a standard tank in a big store. However, you need to also consider the shipping charges. Unless you live nearby and can pick the tank up yourself (or have it shipped to your LFS at a cut rate), the shipping charge alone may add considerable cost, especially for larger tanks.
But don't let any additional cost stop you from owning that beautiful showpiece that you've always wanted. Do your homework before selecting the design of your tank and then do your homework on who to get to build it. Below are a few tank vendors that can accommodate your need for that special tank build (Disclaimer: I've never used any of these vendors and thus can't speak for the quality of their work. I'm not endorsing them in any way, only providing links to their sites as a resource for you, the reader).
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub