From a gaming perspective, 2x4GB will be a much better route than 1x8GB.
Right now, I'd actually go with first Gen Ryzen, given the price drops - however, remember Zen2 launches soon, and that'll either provide your friend with better performance, or (very likely) a lower price on the older stuff.
6c/12t, RX580 and 2x8GB @ 3000MHz:
PCPartPicker Part List
CPU: AMD - Ryzen 5 1600 3.2 GHz 6-Core Processor (€110.00 @ Amazon Deutschland)
Motherboard: Gigabyte - GA-AX370M-Gaming 3 Micro ATX AM4 Motherboard (€68.90 @ Amazon Deutschland)
Memory: G.Skill - Aegis 16 GB (2 x 8 GB) DDR4-3000 Memory (€69.09 @ Amazon Deutschland)
Storage: Patriot - Burst 480 GB 2.5" Solid State Drive (€47.99 @ Amazon Deutschland)
Video Card: XFX - Radeon RX 580 8 GB GTS XXX ED Video Card (€179.00 @ Amazon Deutschland)
Case: Cougar - MX330 ATX Mid Tower Case (€34.90 @ Amazon Deutschland)
Power Supply: Corsair - CXM 550 W 80+ Bronze Certified Semi-modular ATX Power Supply (€64.98 @ Amazon Deutschland)
Total: €574.86
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-06-24 22:48 CEST+0200
Can still make second Gen work within budget too
PCPartPicker Part List
CPU: AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor (€135.89 @ Amazon Deutschland)
Motherboard: ASRock - B450M-HDV R4.0 Micro ATX AM4 Motherboard (€65.99 @ Amazon Deutschland)
Memory: G.Skill - Aegis 16 GB (2 x 8 GB) DDR4-3000 Memory (€69.09 @ Amazon Deutschland)
Storage: Patriot - Burst 480 GB 2.5" Solid State Drive (€47.99 @ Amazon Deutschland)
Video Card: XFX - Radeon RX 580 8 GB GTS XXX ED Video Card (€179.00 @ Amazon Deutschland)
Case: Cougar - MX330 ATX Mid Tower Case (€34.90 @ Amazon Deutschland)
Power Supply: Corsair - CXM 550 W 80+ Bronze Certified Semi-modular ATX Power Supply (€64.98 @ Amazon Deutschland)
Total: €597.84
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-06-24 22:49 CEST+0200