To create a line graph, you can use the User Field graph. Simply create a Task User Field in the Navigator->User Fields panel, and assign these fields to your selected tasks; assigning specific values and colour coding as necessary: 

1. Create a Task User Field of Integer or Number Type to hold your graph values
2. Assign the User Field to the relevant Tasks, providing a specific value in the Task Properties>User Fields panel or by adding the User Field column to the Task List. Alternatively, User Field values can be calculated using Formulas. The User Field value will represent the height of the bar on the graph
   
3. Open the User Field Graph window from the Windows ribbon
4. Make sure to enable the check box next to the User Field name in the User Fields list panel to see the values in the graph. You can enable more than one User Field if desired for comparison purposes
   
5. You can edit the graph colour in Navigator>User Fields under Graph Values: Colour
   
6. Right click in the User Field Graph to turn the Legend on or off. You can also choose which tasks to include the graph: All Tasks, Selected Tasks, or Filtered Tasks.