I like pc part picker:
https://pcpartpicker.com/guide/
That gives you a range of common systems that people right now are considering state of the art and best buys for what you get.
I would recommend you read all three parts of this article:
https://www.techspot.com/article/1561-build-a-pc-bad-idea-ddr4-memory/
Because right now REALLY SUCKS when you are trying to buy good computer parts.
Sorry to give you the bad news, but right now the bitcoin mining rigs have made the good graphics cards really, really expensive now. A good graphics card like the Nvidia 1050 could be bought for $200 last April. Now it is selling for $400. It is a horrible time to try to upgrade your computer or buy a good gaming computer.
It can be done... but for what you get you will be paying a lot more than you would have a year ago.
I personally am limping along, hoping that the mining craze crashes and hundreds of good 'lightly used' graphics cards get sold on ebay for bargain prices.