Using shape editing tools.
Revit roof secrets.
Please like this video.
Then choose attach top base 2 and finally select the roof 3.
Roof by footprint can be used for both flat and sloped pitched roofs.
In the option bar make sure defines slope is activated for boundary lines.
We can use the same attach top base tool to tidy up this junction.
Discover free revit bim objects for roofs.
I believe this tools are not design for this purpose.
Once again select the wall first 1.
See hd version of video tutorial here.
For creating complex roof it might be easier if you create separate roof then use join roof tool to join them later.
Revit then makes the wall meet the underside of the roof correctly.
But i m not really sure if this is a best practice.
You need to create the bay window roof separately.
To turn a sloped roof into a flat roof select all roof boundaries purple lines and uncheck defines slope in the option bar.