It was the same for me. Turns out my pc had not auto updated the the big Nov update. Had to do it manually and now its bought and downloading.
Had to use the media creation tool to update.
Its a great game, perfect for hangover gaming or a normal game if you enjoy chilled city building
Well I made up a Ukraine post code
I did this:
Change your PC's region to Ukraine
Go to the windows 10 store on your app list and search for Rise of the Tomb Raider
Buy it with your credit card (you'll have to sign in with your microsoft account, or make a new one) and invent an address with a postcode matching the format Jono just posted
Stop or cancel the download and change your region back to UK
Not sure if you have to do the last step, but I did and it worked with the download almost finished at this moment.
Start downloading again
Nope.
You will be playing it while logged into xbox live though.
Yeah, I couldn't find an option to download to a drive other than C.
Would've preferred it elsewhere too.
ED: Here you go http://www.tenforums.com/tutorials/6422-apps-save-location-change-windows-10-a.html
Hmmm I got my Windows 10 updated and I can now buy via Ukraine....but it seems dodgy putting in a fake address and your card number....don't want account or card to be blocked.....hmmmm