Perspective can be a challenge when you are first learning to draw architecture for several reasons. One reason is that a building may look simple as you stand in front of it, but when you try to draw it, the lines get confusing and the dimensions shift. This is because your eye compensates for perspective, but your pencil does not.
Another reason is that many beginning architectural drawing students assume that they need to understand complex perspective drawing systems. This can make architectural drawing much more complicated than it needs to be. You will find it much simpler to draw using perspective if you pay attention to how the horizontal lines of the building appear to move as you look down the length of it.
For example, when you stand at the top of a street or at the end of a long hall, you can see how the lines along the roof, the sidewalk, and the tops and bottoms of rows of windows all seem to be tilting to one side. This is perspective. When you first start practicing perspective, try this exercise. Choose a quiet corner of a room to sit in, and look up at the juncture where the two walls meet the ceiling. Rather than trying to draw the whole room, simply draw the lines where the tops of the walls meet the ceiling. Both of these lines will be tilting toward some point at eye level.
Take 10 or 15 minutes to very lightly sketch these lines with your pencil, tilting them until they look like what you see. You do not need to draw any of the furniture in the room. You just want to get the feeling of how the planes seem to tilt toward a vanishing point. When you are learning to draw architectural subjects using perspective, you may find that you tend to make all the lines either horizontal or vertical. While there are many straight lines in a building, when you draw it in perspective, these lines will not appear straight.
If you draw the lines along the roof or the tops of the windows of a long building so that they remain parallel, the building will look flat or distorted. To correct this, try very lightly extending the lines of the roof or the windows until they intersect somewhere off the page. This will help you see the direction these lines want to go. Once you can see the direction, you can re-draw the building, using the correct lines instead of guessing at them.
Here is another technique that can help you get a feeling for perspective. Try re-drawing the same perspective sketch two or three times, each time making the lines a little different. For example, you might want to draw a block-shaped building from the corner. First draw the front of the building, and then slowly tilt the lines of the end of the building as you draw it, until it intersects with the vanishing point. Then try drawing the building again, this time making the tilt of the lines a little more extreme.
Do this several times, until you get a feeling for what looks right. Comparing the different sketches will help you develop your critical ability much faster than drawing a single sketch and trying to make it perfect. As you practice and get used to seeing the way the lines tilt, you will find that perspective is not that mysterious after all. You will be drawing architecture successfully, using what you observe to guide your pencil.