Building a PC for friends first ever gaming pc need help please

Budget- £350
Currency- GBP
Retailer- Any, preferably UK based
I need the computer for £350 and a good cheapish monitor with keyboard and mouse for £150
Use- Casual gaming
Overclock- if possible yes
Water-cool- No
Fps- As much I can get.
Resolution- 1080p
Games- garys mod, gta iv (with mods), all the fun ones... etc
with windows 8.1 included in budget
If you would use pcpartpicker thank you

Here's the best I could do with your budget, if you have any questions and/or concerns feel free to ask.

The Build: http://uk.pcpartpicker.com/p/W48hNG

would an r7 370 be overkill or would it be worth it to last a couple of years?

Alright, there's a place doing a 21.5 inch DVI Acer panel that's alright (have one myself) for £60 at the moment, so that's cut down costs quite a bit. I've added it in as a custom part. Tried to fit a 380 in there, it's just under a tenner over budget.

http://uk.pcpartpicker.com/p/LXLWTW

SCAN's pretty deceptive FYI, upfront, their prices look the best, but then there's delivery on pretty much anything.

An APU build with an A8 7650K may be your best bet, ill update in a bit, it won't max things out at 1080p 60fps, but you can always throw in a GPU later, my current system is all run off a 5800K APU at 1080p without much issue, though I mainly play not too intensive games anyways.

Here's my suggestion anyways, total comes to £278.59 before the monitor/mouse/keyboard/audio set up
http://uk.pcpartpicker.com/p/B8r9ZL

Expanding a bit on that Here's a build with an 860K+R9 270, You may want to double check on that monitor retailer, but for 30 dollars more than the lowest 1080p IPS display I saw you could get a 21:9, although the latency is a bit higher which in all likely hood wouldn't be noticeable anyways, and if 4GBs of RAM isn't enough throwing in another stick when he has an extra 30 bucks lying around is easy enough.

http://uk.pcpartpicker.com/p/CQPbQ7

Update:

http://uk.pcpartpicker.com/p/xvj83C

Went for the non-semi modular version of that PSU to take the price down a notch and bring it under budget.

Here's where you can grab that monitor: HYPERLINK WOA

You might be able to pick up a second hand HD7950 or R9 280 for ~100 GBP, (might even be able to run two if you got a more powerful power supply). As for RAM, yes you do need 8GB these days, can't really get by too well with less than that.

If you aren't doing anything too intensive 4gbs is fine, especially if it's the difference in getting other components that are a bit better and it's the easiest upgrade you could do

Considering you can grab a 8GB stick for like £35 nowadays I don't think you'd save much from going with a single 4 (£15 maybe). I mean sure, if you really need that extra cash elsewhere, do it, but IMO the amount saved doesn't really outweigh the 50% reduction in RAM capacity.