Help me get a decent PC

Hey, I have been playing games for all my life, my current PC is over 10+ years old by now and struggles with pretty much everything. Most of the time a new game comes out that I would like to play, I have to tell my friends that my PC probably can't handle it. And go back to old games that still work. I can't afford to get a decent one since the money is tight, so I'm trying out this way, if someone is so kind to help me out.

I would build the pc myself, since that is the cheapest way. I would gladly document some of the results that come of this.