I'm building my first computer for blender and still don't know what i should buy

My budget is $900 American max.

I want to build a computer because I heard you can have a cheaper/better computer if you built everything yourself.
Please only answer this question if you know Blender well and how it works.
If you want to recommend me a motherboard to use that’s fine. I heard that high poly really only use virtual ram.
Is that true?

Well it all depends what you wann do (modelling maybe even only low poly to sculpting mega high poly, cinematic material research, video fx… ). I use blender since version 2.4x (yes back in 200x ) for some years now fro my personal amusement and i build my PC myself in the past (job education in electronics)… currently using just a i3-3220 8GB on linux for 55€ (2.93 and 3.0alpha do run ) processor intern graphics (former office PC). And if you just heard something like:

Maybe you don’t understand enough of PC’s (why use only and what would be the consequence)??? And it would be a good idea do just use it on an older PC and see for what you really need?