Hi Marwan,
I'm afraid there isn't a fully automatic way to generate the desired slice. When using the Auto align feature in the Extend X/Y Size to Area mode, it rotates the corresponding array, resulting in such a slice. Disabling the Auto align feature can achieve the desired slice, but it will also slice the bottom. Therefore, manually using the Slice modifier (and Cap Holes, if needed) is the recommended approach in this case.
Best regards,
You can do this with a DistanceTex. Draw a box (or you can even use railclone to scale a box along the splines with a certain ID to do it completely parametrically) where the ridge is and what you want to have cut, similarly how you would do it for a boolean. But instead of a Boolean you use a VrayDistanceTex as a mask for the opacity (granted if you use Vray, I'm sure other render engines have a similar map).
- Create your roof material and put a distance tex map in the opacity slot
- Use that box as an object in the distance tex
- Set the distance to 0, far color white, near color black, inside seperate and inside solid enabled, set the color of the inside to black
- Hide the box or railclone or make it none renderable
- Profit
If you use V-Ray it could be that you might have some artifacts (black patches) if you have a lot of overlapping opacity going on, then just raise the Max Transparency Levels in the render settings under Global Switches (Advanced)