Is this PC build good ?

CPU + MB - As Casper said, you have a mismatch between a K-series CPU meant for overclocking paired with a non-overclocking B250 chipset motherboard. At the moment, if you are looking to overclock check out the Z370 chipset paired with the 8600k. If you are not looking to overclock, look toward the i7-7700 / i5-7500 paired with a B250 or H270 chipset board. ...or you can wait a few months for the newer B360 and H370 boards (not released yet) to match the new i5-8400 / i5-8500.
MEM - Always install modules in matching pairs to take advantage of the dual memory controllers. A single module, or mismatching modules, will have you in single channel mode (reduced performance). Best to go with a MB with four memory slots. Two now, and two to fill down the road for a potential upgrade.
SSD - For a $1200 build, consider adding an SSD.
PSU - The Corsair CX lineup is ok at best. Stick with a Tier 1 or Tier 2 unit. You get what you pay for here so don't cheap out... Look toward XFX, Seasonic, or the EVGA lineups in the link below. http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i5-7500 3.4GHz Quad-Core Processor ($184.49 @ SuperBiiz)
Motherboard: ASRock - B250M Pro4 Micro ATX LGA1151 Motherboard ($60.98 @ Newegg)
Memory: G.Skill - NT Series 8GB (2 x 4GB) DDR4-2400 Memory ($80.99 @ Newegg)
Storage: Crucial - MX300 275GB M.2-2280 Solid State Drive ($92.88 @ OutletPC)
Storage: Western Digital - Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($45.69 @ OutletPC)
Video Card: EVGA - GeForce GTX 1080 8GB SC2 Gaming iCX Video Card ($550.98 @ Amazon)
Case: Corsair - 200R ATX Mid Tower Case ($59.99 @ Amazon)
Power Supply: EVGA - 650W 80+ Gold Certified Semi-Modular ATX Power Supply ($71.99 @ SuperBiiz)
Case Fan: Corsair - Air Series AF120 Performance Edition (2-Pack) 63.5 CFM 120mm Fans ($26.89 @ OutletPC)
Total: $1174.88