Costco XPS 8700 Desktop vs Building

The Costco Dell doesn't give enough detaiul:

Brand: Dell
Graphic Card: NVIDIA GeForce GTX 745
Hard Drive Size: 1 TB
Monitor: Monitor Not Included
Operating System: Windows 8.1
Optical Drive: DVD±RW
Processor: Intel Core i7
RAM Included: 16 GB

CPU: Intel Core i5-4690K 3.5GHz Quad-Core Processor ($229.99 @ SuperBiiz)
Motherboard: Asus Sabertooth Z87 ATX LGA1150 Motherboard ($127.89 @ OutletPC)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory ($48.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($52.49 @ OutletPC)
Video Card: MSI Radeon R9 380 4GB Video Card ($239.98 @ SuperBiiz)
Case: Corsair 730T Black ATX Full Tower Case ($109.99 @ Newegg)
Power Supply: Corsair Builder 600W 80+ Bronze Certified ATX Power Supply ($44.99 @ Newegg)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($18.89 @ OutletPC)
Total: $873.21

I think your build will be much better value. But I'd cut down on the case cost and get a better PSU. And I'd change the Z87 mobo to an ASRock z97 Extreme 4 - http://www.newegg.com/Product/Product.aspx?Item=N82E16813157503 and with the money saved get a Cryorig H7 CPU cooler.
 
I personally wouldn't go with either - those prebuilts at Costco are generally junk, and you can get much better for your budget if you do something like this:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4690K 3.5GHz Quad-Core Processor ($259.86 @ OutletPC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($26.98 @ OutletPC)
Motherboard: MSI Z97-GAMING 5 ATX LGA1150 Motherboard ($139.99 @ SuperBiiz)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-2400 Memory ($59.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($52.49 @ OutletPC)
Video Card: Asus GeForce GTX 970 4GB STRIX Video Card ($319.99 @ SuperBiiz)
Case: Corsair 200R ATX Mid Tower Case ($59.99 @ Micro Center)
Power Supply: EVGA SuperNOVA GS 550W 80+ Gold Certified Fully-Modular ATX Power Supply ($65.98 @ Newegg)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer ($14.98 @ OutletPC)
Total: $1000.25
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-07-07 20:20 EDT-0400

That will be a far wiser use of $1K than either system you picked would be. I also wouldn't touch the Corsair Builder series with a 10 foot pole.
 
No to the Dell and that build. The pcpartpicker build you have Z87 board when you should have a Z97 board, and poor quality power supply. Overly expensive case. Your price, to performance, is just not good, either way.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($176.95 @ SuperBiiz)
Motherboard: ASRock H97 PRO4 ATX LGA1150 Motherboard ($81.89 @ OutletPC)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory ($44.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($52.49 @ OutletPC)
Video Card: EVGA GeForce GTX 970 4GB ACX 2.0 Video Card ($326.99 @ SuperBiiz)
Case: Corsair 200R ATX Mid Tower Case ($59.99 @ Micro Center)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($58.99 @ SuperBiiz)
Optical Drive: LG GH24NSC0B DVD/CD Writer ($12.99 @ Newegg)
Total: $815.28
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-07-28 14:43 EDT-0400