I worked on a minecraft “clone” in unity and you will not place a real block.
You would more likely calculate each side of a block. Than you would need
to define blocktypes by numbers. Each blocktype uses different graphics for
the block sides. You also need to point out what side is really visible for the
player.
In minecraft, only the visible sides are drawn. If you delete a block, it’s not
really deleted. It was changed to the air blocktype. So you want a block side
only be drawn if its next to an air block.
The minecraft world is just a NxNxN “array” with numbers in it. And you draw
the sides of the blocks only if an air block is near. Everything else is invisble.
Otherwise your framerate would go to 0 in an instant.
Look up videos of Notch first trys on setting up the minecraft world.
I don’t know how you can do this in UE4, but in Unity i calculated every point,
triangle and UVs manualy.