Use 3 point perspective to build a block with a simple cutout.

Place two vanishing points on the horizon line, and one vanishing point at the bottom of the page.

Place a dot - the closest corner of the block.

Connect the dot with all three vanishing points.

Mark the back corners of the block

Draw 2 receding lines from the bottom vanishing point to the back corners of the block.

Draw 2 receding lines from left and right vanishing points to the back corners of the block.

The block is done now.

Outline the visible parts of the block.

Divide the three closest corners into grid marks.

You can use the "post" method or "eyeball" the marks reducing the space between them as you move away from the front corner.

Connect each mark with at least two of the vanishing points.

Now, that the block is done...

Mark a cutout area.

Erase everything inside it.

Define the three visible inside surfaces - draw the three receding lines through the corners.

Pick a side in the cutout ares:

From the points, where the grid-lines stop at the edge of the cutout - draw receding lines.

Repeat the step on the other side.

Now the bottom side of the cutout is completed.

Repeat the steps on the other two surfaces of the cutout.

Complete the drawing by outlining all visible parts and coloring.

Finished drawing