First build draft

hello everyone, this is my first post so im pretty new to all this stuff. I would like my computer to play BF3 at a good setting  

Approximate Purchase Date: e.g.: this month

Budget Range: £850=$1325

System Usage from Most to Least Important: gaming, watching youtub vidoes

Are you buying a monitor: Yes

Do you need to buy OS: no

Preferred Website(s) for Parts: english sites please

Location: england

Parts Preferences: i don't mind

Overclocking: Maybe if i could get a better graphics card and not overclock then overclocking wouldn't be needed

SLI or Crossfire: Maybe

Your Monitor Resolution: 1920x1080

thanks for any replies