The only good way to get what you want is to build one.
It's also a good exercise.
Fully agree, however building your own PC requires you to have some technical skill.
If you want something that is fairly future proof decide on your motherboard and it's features first - don't do this on the cheap although there is probably little need to to spend too much either. Obviously some home work is essential here and that means using the web to browse forums and get technical specifications.
Once you decide on your motherboard decide on your processor that is compatible with that motherboard. Next you need to decide on your RAM size and if you are going to go for DDR3 or DDR4. Again check your motherboard support and this is the reason why I said don't scrimp on this.
Now you are ready to decide on your disks and I do suggest a 60GB or 120GB (preferred) or 240GB SSD for your system disk and a 3.5" 7200rpm or better HDD in a size that you require and is within your budget for your main storage. Getting two or more HHD's is fine but this begs the question do you really need it? The same goes for large capacity SSD's and of course these are not cheap.
At this stage we can decide on a few extra things although you should have decided earlier such as a monitor, wireless card/dongle, keyboard and mouse as well as a case with a power supply that has at the very least 20% or more power to support all your parts. Bright lights and discotheque for your case is optional and surprisingly inexpensive although IMHO very distracting.
Anyone that has read this far will notice that I have not mentioned a graphics card. Some mother boards do have a graphics card which will support 1080p and even some 4k monitors so you may not need a separate graphics card for general computer use. Buying a graphics card depends on what monitor you want and your motherboard (yep I'm back there again) support and this can really blow out your budget so be aware. If you are into serious gaming then a good keyboard and mouse are essential so it is not a good idea to cheap out on these.
Now for the operating system. That is entirely up to you, Linux distributions are free and can pretty much do most things people want although that is subjective. Microsoft OS's are not free although some people are fine with a green parrot and peg leg with rum optional, although in this case it does help ease your conscience.