Sloping Wall for Skylight

[BugFinder]

I have a skylight in the roof which has a casement (not sure of the correct name) which leads down to the ceiling.

I would like to know how to create a sloping wall perpendicular to the roof as in the image below:

I need to create the wall where the red lines are shown and connect side walls to it.  Note: I haven't created the cutout in the ceiling yet!!

Revit file is atttached.

Thanks

[barthbradley]

Use the Roof Tool to create this wall.

[barthbradley]

...or Mass the opening and use the Wall by Face tool to create Walls.  

[martijn_pater]

If it's just this wall you could also model it in-place under wall category, multi-layered/parametric if you like...

[BugFinder]

@barthbradleyI've managed to get the walls as you suggested using the mass and the wall by face tool but I'm left with the following where the walls don't meet the roof:

Now, normally I'd use the attach top/base tool but this does not appear as an option for me; I suppose it is due to the way it was created.

Are there any tools which would fix this issue?

Thanks

[ToanDN]

Join geometry the wall and the roof.

[barthbradley]

I would edit the Mass and make it taller (start it from top surface of Roof), Update to Face the Walls, and then In-Place Model a Void Extrusion to cut all the Walls flush to the bottom surface of the Roof.  

[BugFinder]

@ToanDNI tried your suggestion to Join geometry but nothing happened - the walls remained in the same place so was left with trying barthbradley's suggestion...

@barthbradleyI was really struggling with editing the mass as it didn't want to play nicely but eventually got there after starting again.  Once I put the walls on it, it came out like this:

with errors saying it couldn't keep the walls joined. What would you normally do here?

Thanks