pls help with my 1st build attempt

Both Z170 and Z270 use DDR4 RAM, so any DDR4 RAM won't cause any incompatibilities. Your build is great, but I will give you some advice to save money:
1) The sweet spot for a GTX 1080 is 750W (650W if it's Founders' Edition). 850W will be a waste except if you're planning on SLI in the future.
2) You will be playing with your PC for years, so the 1 game argument is most likely invalid. You're going to need more storage than 256GB. My advice for this is to run Triple Drive Setup. Buy 128GB M.2 PCI-E SSD for Boot Drive and crucial programs, 256/512GB for games, and 1/2TB for Media Storage.
3) It all comes back to preferences, but you can get a better case for a cheaper price. Try searching for Phanteks Eclipse P400s, Corsair 400C, and NZXT S340 (some of my favorite cases).

If you're going to get an m.2 ssd, get it at the start of the build, it's a difficult part to add into a completed build.

Ripjaws is budget ram, GSkill TridentZ on the other hand is good stuff.

Crucial Ballistix is also a good option.
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=Ballistix&ignorear=0&N=100007611%20601190328%20600006072&isNodeId=1
You'll likely only need 16GB of ram for now, and can always add more later off if you need it.
I actually have the "grey" model, which actually has a very nice brushed-aluminum finish on the top, and is more color-neutral than it looks in the photos once you install it.
So far, I've had mine for nearly a year, and it seems to be holding up well for being mid-ranged ram.

As far as cases are concerned, I would suggest a Corsair Vengence C70 instead:
https://www.newegg.com/Product/Product.aspx?Item=N82E16811139013&cm_re=Corsair_Case-_-11-139-013-_-Product
It's a bit of an older case, but the support for topmounting radiators is much better.
I personally own a C70, as well as the 780T and it's little M-ITX brother the 380T(as a travel rig),
and another one of it's problems is that the restart button is very easy to hit on accident, as it's very out in the open, and as large as the fan control button on the IO panel.
The C70 is much better in this regard as it actually has a little protective cover for the restart button.
A sort of minor + , but still something to keep in mind.
If you are into the military-chic look, there is also a green option for the C70 as well.

On PSU, would strongly recommend a Corsair RM750X over the EVGA G2 850W.
I know they are the same price(at least on Newegg), and the Corsair is 100 Watts less,
but the Corsair PSU is UL certified, which is usually a mark of more safety/quality engineering and manufacturing standards. (I have a CS/Electrical Engineering background).
In my experience, UL cert PSUs are much more reliable and have a much smaller chance to fail or develop things like coil whine over the long-term.

As far as cooling, stick to the Corsair H100i V2.
While they may not perform on paper as well as some of the other coolers out there,
they tend to be less leak-prone(But not leak-proof mind you), and have less instances of pump failure.
With that being said, you might want to consider looking at some high-end air coolers(Like a bequiet! or as an alternative, with this being your first rig and all. As if G-d forbid you do ever get a leak, and it ruins your CPU and Motherboard, you may be without a PC for a while if you don't have the money on hand to get replacements.

A Titan X (Pascal) would draw 275W at most, so you'll still have plenty. But nVidia is poised to release the GTX 1080 Ti soon, if you haven't bought the standard GTX 1080 yet, then the Ti version would probably be better pick than the Titan X; if you already bought a GTX 1080 then unless you have very specific demands for the build, neither the Ti nor the Titan X produces enough performance benefits that is worthy of the price differences.