Here are the steps to create a floor plan of an octagonal old house with the right measures of angles and lengths of the walls on the plan:
1. Start by drawing a large octagon in the center of the paper. Determine the overall size of the house, keeping in mind the scale of the drawing.
2. Draw lines connecting each of the octagon's eight vertices to create eight triangular sections.
3. Each of these triangles will become a different room in the house. Determine the size and shape of each of the rooms. Be sure to include doors, windows, and furniture.
4. Measure the angles of the octagon to ensure they are equal. Each angle in an octagon should measure 135 degrees.
5. Measure the length of the walls on the plan. The length of each wall will depend on the overall size of the house and the size of each room.
6. Use appropriate marks to show congruent angles and segments. Label all points in the diagram where the walls intersect.
7. Add any additional features to the floor plan, such as stairs, porches, or chimneys, as needed.
Remember to include a compass rose or north arrow to show the orientation of the house.