I would advise against building your own if you don't have a lot of time to research things properly. People who build computers make it sound easy, but it's not. I've put together a few computers through the years (my first was a kit with 2K of memory, but I bought the expansion pack to get 4K), done some electronics and such (built a nice tube amp) and was a motorcycle and snowmobile mechanic for a few years, as well as a software designer for a few more.
All that to say that I did not find my latest computer build to be easy at all. It took at least six months to get up to date with what had happened with computers since the last time I built one, to learn who made what, who was good, who wasn't, where to buy, where not to buy, water cooling or air cooling, voltage controlled fans or PWM fans, Sata II or Sata III... The list goes on and on. It can be a lot of fun, but it has to become a hobby. The advantage of taking your time is you can buy items when they go on sale. I saved hundreds of dollars by waiting for the right moment to buy each part.
The actual assembly in my case took a couple of weekends, say four full days. There again, some prior experience with fasteners, wiring and circuit boards is useful. How tight do you tighten the CPU cooler screws ? Even I had no clue. I have a good idea of how much strain a fastener can take, but I have no idea how much a CPU socket can take. I'd have to break a few to know. And the thing loosens with time and temperature changes, at least at first.
And that's only to build the computer. It will then take days and days to install all the drivers and software and figure out what's happening when things don't work. Took me a good month to get most stuff installed and running the way I like, I'm still not completely done.
The whole process is so complex, involving so many components from so many different manufacturers, that I'm continuously amazed that my system runs at all.
If I wasn't prepared to go to all this trouble I'd buy a business Dell, like I've done in the past. With the three-year on-site warranty so you can let them worry about the problems. If the system lasts three years it will probably last ten, like my previous Dell desktop which is still running daily.
If you do go ahead and build your own, good luck. It's quiet an experience and very rewarding when you're done. It's taken up so much of my time this past year that now I have to ask myself, what now ? The answer in my case is : play Sonar !