To-date, based on my (and others') personal experience, I recommend the following components for anyone's next gaming PC.
1. CPU i7 7700K (7th generation) or i7 8700K (8th generation)
2. Asus Motherboards: Z100 or Z200 series for i7 7700K (both Z100 and Z200 are compatible with 7th generation processors)
Asus Motherboard series Z300 for i7 8700K (Z300 series is strictly for 8th generation processors)
Warning: Do not make the mistake of buying a Z300 series motherboard for 7th generation Intel Processors.
Video: EVGA 1070 (any model for a mid tower) This Video Card has all anyone will ever need for 1920 x 1080 screen/game resolution. Also good for 4K.
RAM: 16 GB 1600 to 3400 MHz
CPU Cooler: Closed Loop Liquid Coolers (CLC) such as Corsair Hydro 60, Hydro H80i and dual fan Hydro 100i. The choice depends on how much you plan to overclock your CPU. Frankly speaking, no one "needs" to overclock the 7th and 8th generation Processors from Intel. However. If overclocking is your hobby, the above mentioned processors have plenty of head room.
Case/Box: Your choice of hundreds. Be sure the case is at least Mid Tower, has USB3.1 and is not "just WiFi". Most desktop users will want to plug an Ethernet Cable into the LAN port on their Router or combo Router/Modem.
Example:
I hope this helps builders of new PC's. And yes, I am biased towards ASUS, Intel and Corsair. Having said that I have the following: Corsair 800 Watt Gold PSU - Corsair Hydro H60 CLC - Corsair Vengeance RAM 16 GB
ASUS Motherboard - ASUS CD/DVD Drive - Intel CPU.
Cases are wonderful to shop for; just plain fun looking at the various designs. I personally own two NZXT 410 Phantoms.
Monitors: Again, hundreds of choices. I suggest making sure yours has a 1 millisecond response time, whatever the brand. I have two BenQ 24" 1MS monitors.