At one time in the past, there was real risk involved in building your own machine. That time is largely past, though it does restrict you to keeping to mainstream component manufacturers. Not that that is bad. The only real issue was warranty. Now you can get the same warranty on parts that the dealer does, so that difference is gone. Doing it yourself does have two big pluses- you save the labor cost of letting someone else do it for you, and secondly, you gain a lot of knowledge about how your system works.
Putting it together isn't hard at all, as long as you follow the usual careful practices. Beware of static, no matter what some people try to tell you.
You can start quite a fight around here by simply asking for recommendations of parts
. I have my own preferences backed up by over 20 years of experience, but even at that point, they aren't the ONLY good choices.
To answer your question, as long as you don't plan on overclocking, you don't have that much to worry about when choosing a CPU. Buy a boxed retail chip and the factory-chosen cooler usually comes with it. Yes, there are things to watch out for: off-brand memory, old, slow hard drives, and power supplies that really don't supply the rated power. If you do your homework and take the time to read things slowly (paying attention to what you read), you won't have many problems.
In the end, you won't spend any more than you would at, say, Newegg, but you'll be a lot better educated and you'll have the satisfaction of saying "Yeah, I bult it myself".
<font color=green>****</font color=green> Never Assume <font color=red>ANYTHING</font color=red> <font color=green>****</font color=green>