Camelot Unchained or "Dark Age of Camelot 2" (...meets Minecraft, on steroids - see the video below) is sandbox MMORPG by Mark Jacobs. Or you can check it's IGN Wiki for quick intro.

Building is 100% free form, and it will matter a lot for the economy and especially for control and defense of conquered territories. This video was made in May by Necromaniak, one of players in alpha tests:

...many, many hours later:

Now, this is rather rough - round & cylindrical shapes, wide choice of textures and some other features are yet to be implemented. Also, buildings are fully destructible - unless built offline or in starting zones.

PS Beta should start in a month or two (but it was delayed earlier, so...) and there will be open beta i.e. free tests before launch. Speaking of which, I'm pretty sure it won't launch before second half of 2017.

PPS Useful link, Camelot Unchained reddit. It's handy for asking questions or just learning about the game, including some controversy -