Things to consider when buying a new pc
1. prebuilt off the shelf gaming pc just unpack plug in and away you go job done ah the pitfalls of that thinking on paper the pc may look ok but on a closer inspection 4gig Gpu ok 8gig ram 2x 4gig sticks mother board only has two slots for ram on the motherboard all ram slots full motherboard is the cheapest that will house that Gpu and Cpu also the power supply is a unbranded one sub £40 450/500 watt psu if you want to upgrade in the future new motherboard with four ram slots new power supply 600/750 watts
faster ram ect the list goes on new power supply needed.
2.look for a local computer shop that can build you a rig to the specification for your budget with the componants you want the more research you do the better watching reviews on cases with good airflow best ram gpu psu best water cooler on youtube by rule of thumb the gpu half is half the cost of your full build or if you can build it yourself you can source the parts from amazon and other places to get the best deals more bang for your buck £$ so to speak.