To begin with I must say, that anyone can to learn to build his own personal computer. Now a days, there is plenty of information available on internet-blogs, forums, tutorials, specialized websites etc.
I've built my first computer 5 years ago. I've been interested in IT from my early teen age, so it has not been difficult to do that task. The most important thing is to explore and theoretically understand the principles of building personal computer's architecture. It may seem difficult at a glance, but its surely not.
Now a days the IT market is changing unbelievably fast. So you must be aware not to confuse picking exact parts when building your own computer (for example, RAM modules can look similar for the amateur, but they are different: DDR, DDR 2, DDR 3 types and other). The same rule applies to picking other parts.
You should be aware not to pick a weak PSU (power supply unit) if your system is gonna be powerful for example, the newest graphic cards consume power considerably.
Why you should build your own system when it's so easy to go and buy one at the shop? The answer is simple. When you build your OWN system you know every aspect of your system, you eliminate the possibility that for example, the motherboard will be picked from "cheap" manufacturer (common trick to reduce final price in PC sellers world) and so on. Also that's very pleasant feeling when you know all about your system and can give consultation to your friend or family.
Don't be scared to begin and you'll see the results will make you happy quick!