What is your budget? It ALL depends on your budget.
Well. the rig i put together on PC Part Picker is $1700. so maybe around $800/$900
I I also I have this if there is a way to make it less. but still play both game on high settings http://pcpartpicker.com/p/sbcKWZ
This should do "okay" on ARK.
Ark is just extremely punishing, unless you want to spend $1600 to play it "well" (but still not very good really)
h1z1 isn't that much of an issue.