It is very common when you are dealing with computers, especially games, to focus on speed. Can I run this and that game and so on? It is an understandable question, but it is not easy to answer. Not in a sentence or a book.
To give you an example: I am currently on an Intel I7 920 CPU-based computer, have 6 GB of RAM and an Nvidia 285gtx graphics card. For performance reasons, this is coupled with 3 x 1 TB hard drives in RAID0. That should be enough, right? Can I play graphically difficult games with maximum settings?
No, I can not do that. The reason for this is that the native resolution of my monitor is 2560 x 1900 pixels. I know it's a stupid example, but it's supposed to illustrate one point. All factors must be taken into account when asking such questions.
There are many more factors that are important when building a good computer than mzh and the amount of RAM. Like this setup that I have here now, this is my second computer running RAID hard drives. The first one didn't go so well. I had 2 of the 3 hard drives fail after a few weeks. It took me a while to understand why, but in the end it turned out that my power supply was of poor quality and did not supply all parts of my computer with even power.
The drives actually ran for a long time with the wrong power consumption and therefore broke relatively quickly. This was so marginal that I could actually hear a difference in the sound of my computer fans. At the time, I had about 6 USB devices connected and powered by the USB ports. When I unplugged everyone, I heard the fans in the computer run faster.
Building a computer from parts is a very fun way to learn more about them in general. However, you need to be interested enough to research and read all of the factors. Not just how much money you can put in your new computer.
Make sure that your parts match the other parts and that you have a good power supply. A good power supply doesn't just mean 1200 watts. Mine was 1200 watts, but it was of poor quality and couldn't even deliver power.