1. Using the pathfinder in illustrator
Mrs ras

2. Complete the silhouette of the building with the pen tool

3. 1. Add a new layer above the building you are adding details too 2
1. Add a new layer above the building you are adding details too 2. toggle off the view of the silhouetted building so you can see through it

4. Use the pen tool and trace the details
Use the pen tool and trace the details. Make sure to complete all shapes, no open shapes!!!

5. Toggle on the silhouetted buidling

6. Using the black selection tool, hold shift and select all detail outlines and silhouetted building shape

7. Window>pathfinder

8. While things are still selected Use the exclude button on the pathfinder

9. Choose a fill

10. Continue adding details and using the pathfinder> exclude