A bit of background on tax
Most countries have both income and consumption taxes. So when you earn money you pay, lets say 25% of that to the government and you get to keep 75%. Now when you spend that you may have to pay another 15% in consumption tax.
So using the example above, if a tradesman wants to get $30 an hour for his time, he needs to charge around $47 an hour. Once consumption tax and income tax are accounted for he gets to keep the $30 (using the example rates above).
But the real kicker is that to pay him that $47 an hour you need to earn around $62, because you also have to pay income tax.
Is it better to hire a tradesperson?
If you are lucky enough to earn significantly more than this tradesman, say $70 an hour, then it makes no sense doing the work yourself unless you gain significant enjoyment out of it - effectively making it a leisure activity.
However if you only earn $20, $30, or even $50 an hour and can work at least as efficiently as the tradesman then it makes sense to do the work yourself. If you earn $30 an hour and it takes you twice as long to do the job then it still makes sense to do it yourself, get the idea?
While tradesmen are usually good at their job, if it is your house you are likely to have prior knowledge that will help you work efficiently.
Overall, if you are a competent DIYer, in my view it is unlikely to make sense employing people to do basic building work. You should of course always hire people where your local regulations require it - electrical work for example.
Many people get into DIY to save money. Perhaps now you have a better understanding of why you can save so much money. Chances are that your tradesperson is better at his trade than you are, but you don't have to pay all the taxes that he does when you work on your own home, and forgone income is not taxable either.