Why do you want to build your own computer?
If it’s to save money, you won’t save much. Particularly if you stick with quality components. (Which you should)
If it’s for the experience or just to build your “perfect” machine, then enjoy. Don’t let time or money be an issue.
What is your level of expertise?
If you get a thrill of satisfaction when you’ve managed to open the case and install a new card. Think again.
There’s a degree of mechanical skill involved in mounting the motherboard and installing power supplies, drives, heatsinks et. al. Cableing can be an adventure and the ability to read broken English is helpful. Understanding the nomenclature and how to handle delicate electronics safely is critical.
I suggest going to a bookseller and finding a book on building your own computer. Augment that by learning to search the web. If your interest is gaming, you can likely find a local group of like minded individuals and some real-time one-on-one support.
Read reviews, follow forums (just read) and even take advantage of the commercial “configure your perfect machine” sites to see what they suggest.
Consider buying a solid bare-bones system and building from there. I’m sure if you search around you can find a n00b build-your-own-pc forum. One complete with FAQs, stickies and helpful moderators.