This is my effort at a build:
........
The total comes to around £795. It gives you a Ryzen 5 1600,16GB of 3200MHZ DDR4,a higher end B350 motherboard,a 275GB Crucial SSD and a good GTX1050 2GB. That should be more than enough to serve as a solid base systems for a few years for gaming,or if he wants to get more into programming,etc. When it comes to non-gaming performance,the Ryzen 5 1600 is actually close to CPUs like the Core i7 6800K overall.
But even that might be OTT.
Another alternative might be this:
https://www.amazon.co.uk/AMD-YD1200B...s=ryzen+3+1200
https://www.ebuyer.com/784964-msi-am...d-b350-pc-mate
Then cut back to 8GB of reasonable speed RAM. That should save you around £165 too.
The Core i3 8100 is also a consideration but it is around £116 from Ebuyer. The cheapest Z370 motherboard is around £110. Remember reviews tend to be for the Core i3 8350k which has much higher clockspeeds and can benefit from MCE in the Z370 boards.
The problem is if you get even a midrange B350 motherboard at £80,thats £53 cheaper going with the Ryzen 1200 and that means you can slot in a Ryzen 5 1400 or Ryzen 5 1500X for around the same money which is generally going to be probably a better long-term choice.
Even Coffee Lake performs best with 2667MHZ to 3000MHZ RAM too,so I don't think RAM will be massively cheaper on the Intel side too.