Don't invest all of your budget in one category like ram (the long metal chips) or cpu (central processing unit, the small flat square metal chip you insert in your motherboard) or gpu (graphics processing unit, the big fat thing with fans built in). If you do, you will create a bottleneck that will limit your pc based on the weakest link. All the parts that a pc needs are: cpu, motherboard, gpu, ram, storage (SSD or HDD), power supply, and a case. [the case isn't absolutely necessary] Additional a cooling system would be needed, either water cooling or lots of fans that can be built into the pc. (The cpu needs it's own separate cooler.)

Other than that you need to understand that you won't necessarily be saving money as compared to buying prebuilt a computer. If you try to build a computer based on one you found in a shop, you will realize there will be a price difference of at least $100 (if you're going for a medium to high end). This however isn't applicable if you still decide to buy Windows and maybe the Microsoft programs as most prebuilt pcs have them preinstalled. Thus you would actually waste money. To counteract this there are a few methods.

1: Just don't activate windows and use it. All that you would be missing out on is the ability to change your wallpapers. There are however awesome programs like Wallpaper Engine that not only allow you to bypa.s.s this, but also use an animated wallpaper. Just method 2 on how to get Microsoft and all other programs.

2: Just download a cracked version. There are enough guides online on how to do this. Just remember to use a vpn. This is the only method on this list to get other programs like Microsoft word, etc for free.

3: It is possible to buy Windows from unofficial sources for quite cheap. This method would however cost you a bit.

Building a pc can be compared to playing with legos but for adults and mistakes can be quite costly. It is extremely easy with a guide, and all you need to do is connect around 10 parts. Just make sure your parts are actually compatible and will fit into your chosen pc case.