I get these notifications in the email - lots of great deals to be found for RAM, SSDs, etc
Newegg and Microcenter, sometimes PNY, mostly Newegg, though,
really! get moar stuff, NO REALLY!!
buy buy buy!! good deals on SSDs, DDR4 RAM, next gen Intel CPUs
And if you want help kitting out a computer, use pcpartpicker
If you want help building a computer, there are loads of videos on newegg and youtube (for instance
just go to Youtube and search for "build a gaming computer" and you'll get lots of options to view.)