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