This is a mid-2019 "refresh build" that I put together for the new AMD Zen 2 Ryzen 7 3700x CPU. This rig handles ultrawide gaming at 3440x1440 comfortably, offering 80-100 FPS in AAA titles at high to maxed out settings. Some thoughts on building process and system tuning:

Used parts: I bought the GPU, Mobo and PSU used on eBay. Just deal with sellers with good feedback and you should be fine. Worst case, eBay Buyer Protection should get you covered. In my opinion, you can save quite a bit by buying last generation hardware (new or used) at a discount, that would perform just as well at present.

CPU Tuning: I've worked with several ASUS AM4 Mobos, and they all seem to pump too much voltage to the CPU by default. I would definitely recommend undervolting so your CPU doesn't run as hot. I've been using a negative 0.1V offset and the system has been stable. However, YMMV so make sure you test and benchmark thoroughly to get the right undervolt setting for your system.

Memory Tuning: If you have trouble getting DOCP working with your memory, the Ryzen DRAM Calculator is your friend. I find this guide by Hardware Unboxed to be very easy to understand and follow. The calculator is also helpful if you want to overclock your RAM.

Cosmetics: I chose the H510i with pre-installed LED strips to give the case some nice internal base lighting. I got these white PSU cable extensions from Asiahorse to "bounce" the red-yellow-gold colors. And finally I replaced the stock case fans with some EZDIY RGB fans with some nice halo effects to complement the AMD Wraith Prism.

Hope you guys like this build. Suggestions/comments/questions are all welcome!