Building computer's right now is pretty pricey due to the price of RAM and GPUs.
For build guides you can check YouTube, there's a plethora available, but I'd honestly recommend just buying something off the shelf right now.
There are however 2 new APUs coming out from AMD, the Ryzen 5 2400 should give pretty decent performance in WoW and Overwatch at 1080p. It's the only thing I can think of for an inexpensive build right now.