How much do you think my Gaming Desktop I built is worth?

Right now, its really anyones guess. I suggest looking around on different websites such as eBay, and seeing how much similar computers are going for. You really never know, one month one like yours may go for $800, the next month it would go for $350. I'm just going to go with about $600, only since it's used and you have a moderate gaming pc. Good luck!