Should aim for a 4k build for that price tag, but even then theres things that are overkill for 4k gaming. Someone here should be able to recommend a high end 4k build + monitor for well within your budget
Playing this on my new PC and its so stunning. I have a 3070ti and it runs 1440p between 60-90 FPS depending on how crowded the area, with ray tracing on and generally high settings. I really like to keep it above 60 as I feel I can tell when it drops below. It feels so immersive to just walk...
My advice - get a good 1440p build with a 27 inch 1440p 144 hz monitor and let your son save for a 2nd monitor. There is no need for 2 monitors straight away. Better to spend the money for the 2nd monitor on building a good pc first before worrying about non enhancing peripherals
What price is it on PCS?
On Currys you can get it foe 299
https://www.currys.co.uk/products/asus-tuf-vg27aq1a-quad-hd-27-ips-lcd-gaming-monitor-black-10220251.html
haha I do work for a tech company so the screen on the right they provided for free, so use left for gaming (ASUS 27' Tuf 1440p 170hz) and the one on the right (HP 1080p 60hz) for discord and OBS etc, seems to work well!
And also then can plug my macbook in to both screens when working from home!
Have a mechanical keyboard on the way too!
Specs:
Case: CORSAIR 4000D AIRFLOW TEMPERED GLASS GAMING CASE
Processor: (CPU)AMD Ryzen 5 5600X Six Core CPU (3.7GHz-4.6GHz/35MB CACHE/AM4)
Motherboard: ASUS® PRIME B550-PLUS (DDR4, USB 3.2, 6Gb/s) - ARGB Ready!
Memory (RAM): 16GB Corsair...
https://www.currys.co.uk/products/asus-tuf-vg27aq1a-quad-hd-27-ips-lcd-gaming-monitor-black-10220251.html#collapseFour
This seems like a good deal too, 1440p 170hz for 280 quid