I'm curious - who regulates the computer building industry and makes a license a requirement?
As most have said you can build computers fairly easily and if you're just doing it as a hobby/for pocket change then that's fine. It's not something I would really recommend as anything more than that - it's also worth remembering that in building the computer you will almost certainly become technical support for these people from then on which can last well beyond the point where you've made any profit on the deal at all.
If I was going to build computers again I'd probably just do so for friends, charge them a reasonable amount (or as I used to do leave it up to them) and then once I'd exhausted that market stop - the returns for trying to expand simply weren't worth the additional effort.
i think what your saying is right just build for friends and see what i get ^^
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of how to make myself a few bob over the summer