I've been using the same off-the-shelf desk for the past 10 years. For the most part it does the trick- it doesn't fall over and holds all the necessary tools - a computer or two, monitors, music keyboard, audio interface, computer keyboard and mouse, speakers- this is a bare minimum of what a composer uses and it all needs to be within reach. To arrange all of this comfortably can be kind of tricky: the music keyboard is bulky and should to be in a position so it feels as natural as playing a piano; the computer keyboard and mouse also need to be in a place that doesn't give me carpal tunnel. Ideally, every tool should be as close to the same horizontal plane as possible and increasingly I've felt that it's time to get a desk that works better for my needs.
There are a couple of companies that make readymade desks for composers, but they tend to be hulking generic corporate-looking things covered in laminate and don't really improve on the ergonomics that I want . There seems to one guy who make desks for all of the top LA composers and, while they are gorgeous pieces of furniture, they are very expensive and tend to be overbuilt. But, they seem to solve the problem: he takes apart the music keyboard so there's no external shell and installs it directly into the desk he builds so there's minimal stuff in the way.
I studied how these high-end desks seem to work and set about designing my own composing desk, albeit a simpler version. After deciding on the dimensions and materials, the construction only took about 3-4 days .