Your competition is CyberPowerPC, iBuyPower, Microcenter, Dell, HP, BestBuy. and whatever is on Amazon/Newegg.
They have the advantage of buying parts by the tens of thousands, with the relevant corporate discounts.
They have the advantage of buying OEM Windows licenses in bulk, from MS, for MUCH less than you can.
They also have a warranty dept. Are you going to answer the phone or text at 2AM?
You're just a regular guy, like all of us out here.
You're buying parts at no more of a discount than anyone else can.
So what value add do you bring?
Convince me to buy one of YOUR PCs.