In order to simplify things this explanation covers the perspective of cubic objects, both square and rectangular, of varying dimensions; it will help with drawing anything from a building to a table, a fence, a road or a room. It avoids many of the more complicated elements of perspective that go into artwork composition.
Perspective is a subject that seems to befuddle us all to a certain extent, but some simple guidelines can increase confidence...
All objects get smaller or recede as they get further away. A stone wall on the side of a road is much smaller nearer to the horizon than it is nearer you. The parallel horizontal lines on a subject converge on the horizon.
Work on the basis that the horizon is at your eye level.
When you start a painting, you make the decision of what is in it…whether you want the horizon high or low on the page, whether you draw more ground or more sky. It then helps to imagine that your paper or canvas is actually a sheet of glass hanging vertically in front of you, transforming that scene into 2D. Having your drawing or painting on an easel at eye level is far more practical and easier for perspective than drawing on a table. Obviously having it right in front of you doesn’t make sense as you can’t see what you are painting!
With all the horizontal lines of cubes and rectangles meeting at a point or points on the horizon, it then really helps to understand that everything above your eye level or the horizon will be sloping downwards, and everything below you or the horizon will slope upwards.
Unless you are close in under a building the vertical lines should mainly be vertical. Just to complicate things…buildings subside, tables are wonky, houses are not necessarily built in a straight line so remember this is just a basic guide to help you.
There is only one clear vanishing point. If you are drawing a tiled floor or a table the vanishing point may be way above the top edge of you paper.
As you move around a building you might see less of the near face of a building and a certain amount of two sides, a corner is nearest to you. The two verticals at each extreme of the building are less tall than the one nearest you. This means you need to use TWO-POINT PERSPECTIVE. Your vanishing point may not be on your paper, they may be well off to the side, so you need to make a judgement about where these points are.