To cast cube-shaped spells,
You select a cube's point of origin, which lies anywhere on a face of the cubic effect.
After looking through a multitude of other questions regarding Thunderwave (see 1, 2, 3), which has a range of self, it seems to be general consensus that you can cast Thunderwave as the picture below shows.
But the thing is, this means you have a range of 5ft for casting it, doesn't it? Your point of origin is the square 5ft in front of you. I just assumed that a range of self meant something like this.
You wouldn't take damage since:
A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise.
In order for both these images to be possible casts of Thunderwave, a range of self and a 5ft are the same. Is this interpretation correct?
PS: I didn't show the cube to have 15ft height, but that's to keep things simple. Assume the cube has the proper height, but for this question, we are focusing on the bottom third of it.