Building your own computer ensures better quality and a more powerful device and can cost far less.
If I had the money, I would without question work to build my own PC. Especially for gaming, since overall the cost to build your own PC is actually cheaper than buying a PC at the store and by name brand PC makers like Apple, Dell, and others.
So if you can save up your money for such, it will be more then worth it.
Buying the parts, and building a PC yourself, will and always has been cheaper overall. If you can get the parts and hardware you need. Since some can be more difficult to get and one needs to hope the parts are not all bought up by scalpers wanting to make money off those who are desperate.
Building a PC for gaming nowadays can be cheap. If I were to build a PC I will build it with upgrading it gradually. If I had money, I would begin with the cheapest setup until I get enough money to upgrade with high end parts.