Before starting work on a building, you must first poses an understanding of perspective. Let's start at the very beginning (if you already have a good grasp of how to use perspective to draw buildings, you can skip ahead to step 14). Let's start with using one point perspective to create cubes. Using a ruler and a 2H or harder pencils, very lightly draw the horizon line (blue line) and the vanishing point (red X).
Next, draw a few squares floating in various places on the page, but not too close the vanishing point.
Draw lines from the vanishing point to the closest corners of each square (red lines). Then close off your cubes by drawing the back line of the cubes (green line), but be sure to stay within the red lines leading to the vanishing point.
Erase your unneeded guidelines leading back to the vanishing point and darken the lines of the cubes. You now have a cube created in one point perspective.
Now let's work on two point perspective. After drawing your horizon line, place two different vanishing points on opposite sides of the horizon line. This time, instead of drawing squares, just draw a few vertical lines floating on the page in various places. These lines will become the front edge of our cubes.
From the tops and bottoms of each line (cube edges), draw lines leading to both vanishing points on the page. It's ok if some of your lines run through each other because they can be erased later.
Now close off the sides of your cube in the same manner as step 3 above. But we are not done, since we still need to draw one more side of each cube.
This is where it gets a tad tricky. To finish off the cubes, we have to draw the third side on all necessary cubes. For any cube floating above the horizon line, we will draw the bottom side of the cube by drawing a lines from the bottom tips of the side edges of the cube leading to the opposite vanishing point. Similarly, for any cube floating beneath the horizon line, we will draw the top side of the cube by drawing a lines from the top tips of the side edges of the cube leading to the opposite vanishing point. Note that any cube who's front edge runs through the horizon line will not require a third edge, as it is hidden from our perspective.
Erase unneeded lines and darken up your cubes if you wish. You now know how to utilize two point perspective, but we also need to learn three point perspective before we can start drawing buildings.
Three point perspective is simple after learning two point perspective. With three point perspective, you simply add a third vanishing point to create a more accurate sense of perspective, especially for things like buildings. Let's start by drawing our horizon line near the bottom of the page and placing two vanishing points on either end of the horizon. Next, draw a third vanishing point near the top of your page. Then draw the front edge of your shape (green line) starting from the third vanishing point running down to the bottom of your page.
Next, determine the location of top and bottom of your shape and draw lines leading to the vanishing points. Do not consider the third vanishing point to be the top of your shape when drawing buildings - the top of your shape should fall somewhere below the third vanishing point.
Finally, we can draw the outer edges of the shape. Determine a location for each outer edge along the bottom line. Draw an outer edge line on either side of the center line leading all the way up to the third vanishing point.
Your three point perspective shape is now complete, and you can erase the unneeded line and darken your shape. This is the foundation to be used for creating buildings. If you wish to draw multiple buildings within the same image, just repeat the above steps and utilize your vanishing points properly. We shall use these basic principles of perspective to create our building.
Now that we have an understanding of how to use perspective to draw buildings, let's work on drawing the famous Flatiron building in New York city. This building is very unique in that it is triangular shaped with one corner of the building being very narrow. At the certain angles, the building looks like it is just one big wall with no additional structure behind it. Because of this, we only need two points of perspective, but they are not the same points we used in step 5. Instead, we need one point to the far left of our horizon line (vanishing point 1), and one point way up at the top of our page (vanishing point 2). I recommend drawing on a large sheet of paper, or taping pieces of scratch paper to your page to allow for greater distance to the vanishing points. Remember to draw very lightly at first so that we can erase lines later after we ink.
We're going to start slowly by only doing one line in this step. You do not have to draw the green line shown in this step. The green represents the location of the second vanishing point in relation to the horizon line. I have only inserted the green line as a guide to demonstrate the location of the line we are actually going to draw, which is the red line. The red line will be the narrow corner of the building which is closest to us. You want to draw the base of the red line starting near the base of the green line and extending all the way up to the second vanishing point. This line will become the front corner of the building.
Now we can draw the roof, base, and far corner of the building. Determine the height of the building (line 1) and where the base of it will be (line 2), and lead them to vanishing point 1. Then draw the far edge leading to vanishing point 2 (line 3). This will create the basic shape of the building for us to use as a foundation. It's ok to draw these lines running longer than they need to be since we can erase unneeded lines later on. Remember, the size of the building should be fairly small in comparison to the work area you are drawing on, which is why we should be working on a large surface.
The front corner of the Flatiron Building is curved, rather than a sharp angle. The curve is made distinctive not only by its windows, but by a groove in the brickwork that runs up the side of the building. Use your ruler to draw a vertical line starting from the base of the building near the front corner, running all the way up to the second vanishing point. This will separate the side of the building from the front curved section. Secondly, the various levels of the Flatiron are separated either by ledges or brickwork, making each floor stand out even without looking at the windows. Place your ruler along the vertical line we just made to evenly measure distances between each level. Note that every other level is slightly taller than the others. For example, if working in centimeters, the second level will be 1 centimeter tall, and the second will be 1.2 centimeters tall, the third 1 cm, the fourth 1.2 cm, etc. The first and top levels are taller than all the rest. Lightly place a small mark or dot along the vertical line as a guide. Then draw a line from each dot leading back to the first vanishing point. You now have the levels separated on the side of the building.
As mentioned above, the front corner of the building actually curved, so we now need to separate the levels of the front building just as we did in the previous step. Simply draw a curved line at the front of each level separation line wrapping around the front of the building. The curves near the base of the building should be "flatter" than the ones near the top. This is also a good opportunity to draw the curvature at the base of the building, and the curvature of the roof. Also draw the tiny bit of visible ledge on the far side of the building's rooftop, which should have a rather steep angle. Take this time to quickly draw in the bottom edge of the roof ledge on the back right side of the building as well.
Windows can be a daunting task, but if you are patient, you will be amazed at how great they make the image look. Without windows, the building will look plain and unfinished. Using the same method as the level separation in step 17, use your ruler to mark the location of the windows along the draw vertical lines starting from the bottom of the fourth level of the building (we will do the larger windows of the lower levels in a later step). Also be sure to insert lines on the front of the building (these ones can extend all the way to ground level).
Now that the vertical window guides are in place, we can do the horizontal lines. Evenly space horizontal lines running back to the first vanishing point to represent the tops and bottoms of each window. For the windows on the front section of the building, use the curved brickwork as a guide.
Use the above methods to draw the windows on the lower floors. Keep in mind the size of these windows vary. Also take this time to do a little more work on the large windows near the top of the building by rounding off the tops of those windows.
Before we go any further, we need to draw in the triangular entrance at the front of the building. Erase your marks at the front base of the building and add on the entrance using the methods we have learned so far.
Now is a good time to inks over your image using a ruler and Micron or Copic markers. Be sure not to ink every single line - only ink the lines that you know will be part of the final image. After you ink the needed lines, go back with a kneaded eraser and erase all your pencils marks. Your image should be nice and clean. The lack of pencil marks will make the image less cluttered and easier for us to add in the final details. Take this opportunity to also ink in all the windows black so that they stand out better. We may have to use some white paint or white ink to make corrections and add further detail later.
The Flatiron has a lot of intricate detail on its facade. Complex brickwork, decorative statues, and decorative detail along the ledges cover the building. Perfectly drawing every piece of detail would be an enormous challenge, so instead, we can use the art of suggestion to allude to the decorative architecture. You don't have to take the time to draw every single piece of detail, just the primary pieces. As mentioned before, you may need to go back with white ink or white paint to cover up some existing line art before drawing in things such as arches.
We can finish the illustration by adding shadows to some of the larger decorative pieces, and give the building a shadow on the ground. Using white in, insert a few air conditioning units in some of the windows and make any needed corrections. And that's how you draw the Flatiron!