Helping Brother In Law do a build. Advice please and thanks!

Solution
First off, what is your BIL trying to achieve with the build? (Gaming, Editing etc).

What resolution monitor is paired with it?

I assume gaming..... probably 1440p?

Based strictly on modifying what you have listed there, I'd make some changes to save some money, and that would be about it.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-7700K 4.2GHz Quad-Core Processor ($338.88 @ OutletPC)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($34.89 @ OutletPC)
Motherboard: MSI Z270 SLI ATX LGA1151 Motherboard ($129.99 @ B&H)
Memory: Team Dark 16GB (2 x 8GB) DDR4-3000 Memory ($109.99 @ Newegg)
Storage: ADATA Ultimate SU800 256GB...
First off, what is your BIL trying to achieve with the build? (Gaming, Editing etc).

What resolution monitor is paired with it?

I assume gaming..... probably 1440p?

Based strictly on modifying what you have listed there, I'd make some changes to save some money, and that would be about it.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-7700K 4.2GHz Quad-Core Processor ($338.88 @ OutletPC)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($34.89 @ OutletPC)
Motherboard: MSI Z270 SLI ATX LGA1151 Motherboard ($129.99 @ B&H)
Memory: Team Dark 16GB (2 x 8GB) DDR4-3000 Memory ($109.99 @ Newegg)
Storage: ADATA Ultimate SU800 256GB 2.5" Solid State Drive ($67.98 @ NCIX US)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($48.66 @ OutletPC)
Video Card: EVGA GeForce GTX 1070 8GB SC GAMING ACX 3.0 Black Edition Video Card ($374.00 @ Amazon)
Case: Corsair 100R ATX Mid Tower Case ($44.99 @ Amazon)
Power Supply: SeaSonic G 550W 80+ Gold Certified Semi-Modular ATX Power Supply ($69.39 @ SuperBiiz)
Optical Drive: LG GH24NSC0B DVD/CD Writer ($16.88 @ OutletPC)
Keyboard: Corsair STRAFE Wired Gaming Keyboard ($79.99 @ Amazon)
Total: $1315.64
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-04-11 13:12 EDT-0400

Saves about $150 while giving you a better CPU cooler, a similar budget SSD (could go better there, for sure), a more 'fit for purpose' PSU and a few other tweaks.

Ultimately, would perform identically - and potentially a little better pushing slightly more of an OC from the CPU..... if that's his thing.
 
Solution
The i7 and 1070 would be a very nice pairing for gaming/streaming - potentially a little overkill, but better than being underpowered/
It would also hold up well for a 1440p upgrade.

Any desire to SLI do you think? If not, you could shave off a little more by dropping the SLI ability from the board:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-7700K 4.2GHz Quad-Core Processor ($338.88 @ OutletPC)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($34.89 @ OutletPC)
Motherboard: MSI Z270-A PRO ATX LGA1151 Motherboard ($99.99 @ Amazon)
Memory: Team Dark 16GB (2 x 8GB) DDR4-3000 Memory ($109.99 @ Newegg)
Storage: ADATA Ultimate SU800 256GB 2.5" Solid State Drive ($67.98 @ NCIX US)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($48.66 @ OutletPC)
Video Card: EVGA GeForce GTX 1070 8GB SC GAMING ACX 3.0 Black Edition Video Card ($374.00 @ Amazon)
Case: Corsair 100R ATX Mid Tower Case ($44.99 @ Amazon)
Power Supply: SeaSonic G 550W 80+ Gold Certified Semi-Modular ATX Power Supply ($69.39 @ SuperBiiz)
Optical Drive: LG GH24NSC0B DVD/CD Writer ($16.88 @ OutletPC)
Keyboard: Corsair STRAFE Wired Gaming Keyboard ($79.99 @ Amazon)
Total: $1285.64
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-04-11 13:37 EDT-0400

 
And as a wildcard I've elected to go with a Ryzen 1700/GTX1080 combination: http://pcpartpicker.com/user/coozie7/saved/#view=MCb6hM

That big Ryzen has 'future' written all over it and don't worry about it's 'poor' 1080 performance, unless your brother-in-law is running a 144Hz display my system will run as fast as any Intel one on a 60Hz 1080 monitor.

Note, I've opted for a huge GPU: A GTX1080, it's MASSIVE overkill for a single 1080 monitor so it'll only make sense to include it if you're CERTAIN your brother-in-law will upgrade his display to at least 2560x1440, or even 4K later, if not you can 'drop' to a GTX1070.

Yep, I like that expensive Phanteks case, it looks good, is spacious, has enormous air and watercooling support and can even be customised inside by removing the drive bays (all of them if you want).

And yes, I've not included a optical drive, nor a Windows licence, but I've stuck with the keyboard and storage solutions.

And here is the same build with an expensive (but oh so cool and quiet) GTX1070: http://pcpartpicker.com/user/coozie7/saved/#view=gFtdCJ