I am always building my own systems because that's my job ( IT field ) and I am building it also for future updates, for example at this time I am upgrading my mobo and bought an PCI ssd with in mind that my cpu is compatible and PSU has that extra power. I prefer building my own because I like to know my system. I am using pre-builds for office use.
My opinion on your topic, learn some basic things of building a simple computer from the scratch, use youtube videos, some great content called LTT.