This option turns off the roof slope extrusion for the line.
How to make roof on revit.
Click architecture tabbuild panelroof drop down roof by footprint.
Your now have a flat roof.
Mass are quite easy to make but using this method might be require a lot of works.
First you can create a mass and create roof by selecting the mass faces.
Select toggle slope defining for each line of the roof outline.
Select the lines of the roof outline and right click over the line.
Select finish roof on the create roof footprint ribbon.
Click architecture tab roof drop down roof by footprint.
To edit roof properties before.
The second option in the list is toggle slope defining.
Get these project files and all advanced 1h courses.
Draw a flat roof.
On the draw panel select a sketch or pick tool.
If your design is quite simple you will not want to spend to much time on your roof.
On the properties palette set the underlay value to 01 store floor.
I will not discuss much about this for now.
Changing slope angle and using slope arrow.
Tutorial on roof construction modeling in revit.