MikeJG

I found this on 3D Warehouse (https://3dwarehouse.sketchup.com/index.html).  It's not exactly right but I hope it works for you.
 
Tube Heater.calibz
 
Here's an exterior spot from the Deck Lighting Bonus Library I rotated for you.
 
Spot Light.calibz
 
 

You may need to rebuild your roofs if you dropped the ceiling height in the room spec./structure tab and nothing happened.
 
If you manually drew the roof planes, and just want them 10" lower, you can open both roof planes, lock the pitch and subtract 10" from the baseline, fascia top, or ridge numbers.
 
Another thing you can do is select the roof planes then use the "Transform/Replicate Object' tool on the bottom toolbar and putting -10 in the Z Delta box.
 
Hope that helps.

I don't have v. 9 anymore but I still have X1.  Hopefully this worked the same on both.
 
Grab the higher roof plane.

 
Select the 'Break Line' tool.

 
Put a break as shown here.

 
Grab the handle at the ridge of the lower planes.

 
Drag that handle down and to the right to make a straight line along the outside of the wall

 
The edges of the lower roof planes may still show through the ceiling.  If so, you can drag the valleys in 3/4" or so.  That will clean up the interior view, however the gap will show on the exterior view.
 
As was said before, don't rebuild your roofs or you will have to do this all over.
 
Hope that helps.
 
Mike