Yeh, there isn't really enough money in doing the fully custom PCs, because you'd have to charge high prices for the work which is basically just to make the computer look pretty.
As said, you'd need a fair bit of experience and decent metal working skills if you were properly going down the modding route.
It is probably just best left as a hobby or a side to a 9-5 as mentioned...
Could always start a business to compliment it though - for example a small computer retailer or repair centre or something like that - or even some form of web design if you're good at that.
The thing is, the people who want custom computers can usually do it themselves, usually want to do it themselves, and usually have a budget where buying the best possible parts will come before paying someone else to tart up the case.
Also - if they do want it tarted up massively, they'll probably have had the ideas themselves about what they want, and the majority of the time will have some idea of how to go about doing it themselves...
All this would end up being a very small client base, where they'd be buying products that would be costing you a lot of time to modify and build - but where they wouldn't be prepared to spend the money you'd actually be wanting for it.
So yeh - you're pretty unlikely to make a career out of modding/building PCs. Get a real job and do it as a hobby
