For gaming computers do you just only need a good processor, ram and graphics card to play good games? Like lets say buy: 8gb memory, core i7 unlocked cpu, HD 7850 gpu, low end cheap motherboard, cheap soundcard, cheap case, Cooler master evo 212 heatsink and 650watt psu.
I'm just wondering if it (the build above) will be able to play the latest games coming out in 4-5years time
I would not get a low end motherboard, they tend to die faster and may not work well with all components. Case is not very important as long as you have enough cooling for the system, a case that can take 3 fans should be good. Soundcard, onboard is fine. PSU, make sure it's a good brand also, a cheap one will probably die fast and would not put out close to it's rated power.