Picking parts for a gaming PC will depend on what games you are looking to play. Most games right now will be fine with a mid level CPU like an Intel i5 or AMD Ryzen 5. Looking at GPUs my personal experience with Nvidia has been the best. I have built over 20 computers and most of them went with a graphics card from Nvidia. If you are not looking to play at 4k or ultra 1440p I would stick in the 2060 or 2070 range for graphics cards with the 2070 being possibly too much. Also, most games will play with 8GB of RAM however, 16 is starting to become more standard. If you go above a 2070 GPU I would look into getting a better CPU to avoid bottlenecks in the system. One more thing to keep in mind is that with the price coming down on SSDs I would look into getting one. Some games even recommend having a solid state drive to run their game off of.