Originally Posted by
Cyrops
There is nothing complicated, there could be unforeseeable issues like compatibility, like others said, where are you from? When I was younger, I would just go to PC store and give them a list of parts I wanted (the brand of CPU, GPU, HDD, etc.) and they would assemble and test to make sure everything works.
Saying that, such a service in US costs around 200USD, while prebuilts are cheaper since they buy parts in bulk for cheap. The downside to prebuilt is that the parts used are usually cheapest ones available, for example a no-name 600W PSU vs a well known 600W