CPU - stick with an i5 at most. you didn't exactly specify a budget, but considering you went with a GTX1050 ti, i imagine it's not a lot. if you're OCing, then you want a K-series processor. otherwise, you're not gonna be overclocking much, and getting a Z170/270 motherboard becomes a wasted investment. optionally, the Ryzen 5's are coming soon so think about taking those into consideration, or if you're willing, wait and see how the Ryzen 3 will do.
motherboard - Z270 if you're getting an intel Kaby Lake (i5-7600K at most) or Skylake (i5-6600K at most) CPUs. if you're considering a Z170 for the price, then it's better you stick with Skylake CPUs, to avoid issues with compatibility. in case you didn't know, if you rather consider getting an AMD Ryzen CPU, you're gonna want it's corresponding overclockable motherboard.
RAM - make sure the motherboard supports the RAM, and go with a dual channel kit. for gaming purposes, 2x4GB is plenty in most cases.
GPU - a 1050ti's good, but if you can afford it, there's the 1060 for consideration. I'm a little out of touch with current GPU performances, but consider looking at AMD's option in case there's a cheaper alternative.
PSU - DON'T cheap out on these. but don't overspend on it either. you haven't given us a budget, so depending on your build, the wattage will differ. naturally, you want something that's certified 80+ bronze at least, and of reliable build quality. unfortunately, i'm out of touch in this department as well, so hopefully someone here can fill you in on what's good nowadays.
a VERY rough idea of what you're looking to get. Again, I'm a little behind on some of the current tech, so maybe someone else will be helpful in tidying this recommendation up;
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i3-7350K 4.2GHz Dual-Core Processor ($179.89 @ OutletPC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.88 @ OutletPC)
Motherboard: ASRock Z270 Pro4 ATX LGA1151 Motherboard ($113.98 @ Newegg)
Memory: Crucial 8GB (2 x 4GB) DDR4-2133 Memory ($55.39 @ OutletPC)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($49.33 @ OutletPC)
Video Card: EVGA GeForce GTX 1050 Ti 4GB ACX 2.0 Video Card ($129.99 @ Newegg)
Case: Corsair 270R ATX Mid Tower Case ($49.99 @ Newegg)
Power Supply: SeaSonic 350W 80+ Bronze Certified ATX Power Supply ($44.99 @ SuperBiiz)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($88.58 @ OutletPC)
Total: $737.02
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-22 04:26 EDT-0400