I considered getting a custom cage, but ultimately decided against it mainly because of the issues presented by wood cages (plus custom cages are very expensive).
With a wood cage, you have to be sure that any wood the chins have access to is safe for them to chew, because they likely will chew it at least a little. You have to be sure it doesn't use any toxic paint, glue, sealants, or anything else that is potentially harmful for your chin on the inside. There's also the potential issue of your chin being able to chew through the wood and escape. Not all chins chew that voraciously....but some do. There have absolutely been reports of chins chewing their way out of beautiful custom wood cages. It's not the norm, but it does happen.
There's also the issue of urine seeping into the wood. Unless your chin pees in a litterbox 100% of the time, odds are you're going to be doing a lot of work sanding down pee spots on a cage mainly made from wood. In a metal cage with wood accessories, it's not that big a deal to sand down or replace the occasional ledge or bridge or house that gets peed on, but when the whole cage is constructed of wood, that's going to mean a whole lot more time and expense to maintain, especially if your chin decides to start peeing everywhere (which is not all that uncommon, mine went from peeing quite reliably in the litterbox to peeing everywhere when I moved her to a new cage).
As far as I know, there's no safe way to "chin-proof" wood. Most of not all wood sealants and varnishes that might protect the wood from pee would be toxic for chins to ingest if they chewed it, and there's really no way to keep them from chewing it.
You could tile the floor of the cage, which would probably help. The way I've seen recommended on here is to cut a sheet of laminated plastic to size to cover the floor (to protect the wood underneath from pee), and then to lie stone or ceramic tiles on top. That allows you to easily pull up the tiles and plastic liner for cleaning, and also protects the wood underneath from any pee that seeps between the tiles. And since the chins don't have access to the plastic liner, they can't chew it. A lot of people use that method to tile the floors of their Critter/Ferret Nation cages, but I'm sure it would also work in a custom cage.
At the end of the day, I opted to just buy a Ferret Nation cage instead of messing around with the hassle and expense of a custom cage. It's plenty big, it's way easier to clean and maintain, and I think it looks perfectly nice. But you have to decide what works best for you and your situation. If you're willing to put in the extra time, money, and effort to acquiring and maintaining a suitable custom cage, it could be a good option.