You can actually copy a picture from the web, paste it into Sketchpad, and then draw over it.

1. Pick one of the pictures below. Hold the mouse down on it and wait until you can choose "Copy this image".
2. Go into Sketchpad and in a blank sketch, choose Edit >> Paste.
3. Using the ray tool, start at the upper front corner of the building and put the ray's control point on the same building line at the back edge.
4. Construct another ray, starting at the bottom front corner of the building and following that line to the back of the building.
5. Construct the intersection of those two rays - this is a vanishing point for this picture.
6. Add some more elements to the drawing.