Building a PC really is not hard. The only part you could possibly have a problem with is installing the CPU on the motherboard. If you are not careful you could bend the fine hair like pins on the motherboard rendering it unusable.
Installing a GPU takes about two or three minutes. installing a hard drive is the same time. You just have to plug in one or two cables per component, and close the case. You go to the manufacturer web site, download the drivers and install them and you are done.
So my recommendation is to get a base hp Z420 machine, upgrade the GPU, Ram, and buy an SSD drive. Avoid installing the CPU, save money and get the case motherboard power supply and CPU for a small price, and then by the rest and install it.
HP z420.
e5-1650 CPU, 32GB ram, $600 this is for an ebay certified machine, if you look on kijiji you can get it for more like $400 or $500
Samsung Evo 860, 500 gb, $129.99
GTX 1080 $620
$1329
Not as cpu intense as the ryzen build, but if you consider that maya is your main sotware, and maya wont use more than 6 cores, for viewport performance and modeling, those extra cores wont be used. The place where those cores is an advantage is in multi threaded applications, and in video editing.
For modeling you want a 4 to 6 core machine with decent single threaded performance. And then you want to decide what your primary software is going to be, and if it supports single or multi core CPU.
The ryzen CPU is 12 core which will be better for video editing it's also faster per core, but the $500 for the CPU alone, is what you pay for a motherboard, case, cpu, power supply all together if you get a used workstation, and you don't have to build it if you get a used hp workstation.
Maya view port performance will be acceptable with the 1650 , 32gb ram hp workstation, and the GTX 1080 card in this build is a far better card than the radeon.
see this link for comparison, and rightully so at twice the price.
https://www.google.ca/imgres?imgurl=https://i.ytimg.com/vi/W7_VISmBdGk/maxresdefault.jpg&imgrefurl=https://www.youtube.com/watch?v%3DW7_VISmBdGk&h=720&w=1280&tbnid=p9DKUCPiIn5tHM:&q=radeon+rx+580+vs+gtx+1080&tbnh=118&tbnw=211&usg=AFrqEzeLqbZcVB2RZ-ZAZMotOiM_RrIGIA&vet=12ahUKEwiJxrqp0qrdAhVs7YMKHVxMBOYQ9QEwAHoECAcQBg..i&docid=d7eMzbTt9Z-7CM&sa=X&ved=2ahUKEwiJxrqp0qrdAhVs7YMKHVxMBOYQ9QEwAHoECAcQBg
You need to take a moment to think about whether this is a GPU rendering, or a CPU rendering machine, and then tailor your spending to match that.
In my experience there is no need for a $500 ryzen CPU to model and animate in maya. It wont be used for rendering if you set up GPU rendering (which everyone is going to now).
The GTX 1080 with GPU Rendering in VRay, and Redshift will be very fast.
See this post on puget systems about rendering configurations.
https://www.pugetsystems.com/solutions/content_creation/rendering.php