These are the important questions you need to ask first, and then build the pc around them.
1. Intel or AMD
2. Form factor
3.b. Are you going to overclock
3.b. Latest gen mobo or previous gen (X570 vs X470 vs B550 vs B450 vs B460 vs Z490 vs Z590 etc etc etc)
3.c. Which Gen CPU (AMD is more flexible than Intel with regards to this, and also plays a role in which mobo to pick up)
4. What sort of GPU are you looking at? New, used? I would argue this should actually be point 1, because knowing what GPU you want and what it costs will give you an indication as to what to look at for the rest of the build.
From there, it's simply a case (lol) of finding a case, adding some storage and Bob's your uncle.
TL;DR - Start with the most important piece, my personal opinion is this is the GPU, know what it's gonna cost, and work your way backwards.
Once you know what's left, you'll start finding parts that suit both your theme and your budget.
Hope that helps.