Box 2 shows a true rectangle but it looks lopsided and the floor is too short. Single story buildings are usually longer than they are tall.
Box 3 shows what the eye sees horizontally wide at the front, narrower at the back, and the box looks better with more depth than box 2.
Box 4 and 5 are the same size in the front and the same depth but the box 5 back rectangle is smaller creating the illusion of greater depth but it still looks distorted.
Box 6 is the same as box 5 except the bottom horizontal lines, front and back, are angled up slightly to the right (exaggerated slightly here for visual effect) creating the appearance of a rectangle. The vertical lines are still vertical. There are times when vertical lines need to be angled but with care because our eyes see parallel vertical lines much better than horizontal ones.
Perspective is like looking down a railroad track where they appear to get closer together in the distance. The railroad tracks, though perfectly flat, appear to climb upward in the distance.
The further away you are from the object the more of it you can see. You can see the floor and the roof even though the front still appears larger than the back, so you can raise the back of the building to see more of the roof and it will still look normal.
When drawing perspectives vertical lines usually remain vertical with adjustments only to the horizontal lines.
It is all about perception so you must position yourself in front of the design and try to visualize what you would see if you were scaled to the same size as the part.
These changes can be made using the node editing and/or distort tool.