He doesn't need a OS license, if your fine with the watermark on the corner of the screen you save some money you can spend else where. Also if you want you can buy way cheaper online.
Meanwhile there's a few tweaks for a better motherboard for overclocking and proper cooling.
PCPartPicker part list:
https://de.pcpartpicker.com/list/gQjBFt
Price breakdown by merchant: https://de.pcpartpicker.com/list/gQjBFt/by_merchant/
CPU: AMD - Ryzen 7 2700X 3.7GHz 8-Core Processor (€321.00 @ Amazon Deutschland)
CPU Cooler: Corsair - H55 57.0 CFM Liquid CPU Cooler (€70.85 @ Amazon Deutschland)
Motherboard: ASRock - Fatal1ty X470 Gaming K4 ATX AM4 Motherboard (€165.99 @ Amazon Deutschland)
Memory: G.Skill - Ripjaws V Series 16GB (2 x 8GB) DDR4-3200 Memory (€145.89 @ Alternate)
Storage: Crucial - MX500 250GB M.2-2280 Solid State Drive (€57.90 @ Amazon Deutschland)
Storage: Seagate - Barracuda 2TB 3.5" 7200RPM Internal Hard Drive (€58.55 @ Amazon Deutschland)
Video Card: Gigabyte - GeForce GTX 1080 Ti 11GB Gaming OC 11G Video Card (€604.99 @ Alternate)
Case: Fractal Design - Focus G (White) ATX Mid Tower Case (€43.99 @ Amazon Deutschland)
Power Supply: SeaSonic - FOCUS Plus Gold 650W 80+ Gold Certified Fully-Modular ATX Power Supply (€94.90 @ Amazon Deutschland)
Total: €1564.06
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-09-07 21:13 CEST+0200