1 Draw the roof of the watchtower. Here the sides are slanted to an apex on top, but you could also draw fixed angle roofs using straight lines. Follow the isometric graph lines to ensure proper perspective.

2 Draw the upper watchtower space. Again, follow the graph lines for perspective.

3 Draw the tower. Make this as thick or thin as needed. Here I made my tower section slightly thinner than the top room.

4 Add details like additional vertical and horizontal lines to indicate the wooden beams that make up the tower structure. A door was also added at the base.

5 Add additional details. In this case windows were added to the upper room and cross beams were added to the tower section.

6 If you wish to add color, add it now. Remember to use two different shades to highlight where the sunrays are striking the structure (with one side of the structure lighter and one darker in tone).