You can easy do this with a single brush and the clipping tool.
Make a brush which has the same sizes in the X and Y directions. And make it long in the Z direction.
Then select the brush, hold control and click on the right mouse button like this:
Dot 1 was my first click, dot 2 was my second click, then hit enter and the brush will be cutted like in the image, do the same on the right side and also from an other camera side-view. Then you'll get a piramide like in your screenshots.