You don't really need to build your own, Digitell, just decide on the most important specifications.  The remainder can be negotiated at the store.
Research what you can eg. OS, graphics cards,  memory, etc. that you want, then go to a store that custom builds PCs and just tell them what you want.
In my country, Australia, these are usually small, so you should check that the store has a
long history behind it, in case you need to use their warranty in future [ and find out first how long the warranty lasts ].  These stores usually give out  price lists of parts and of PCs with "recommended_configurations" and provide free quotes for your preferred PC configuration.

You can save money on keeping your current monitor, keyboard, and mouse, too.