I can do it using two "flat" prims, path-cut between 0.5 adn 1.0, but I'm wondering if there is a better way using a cube, or some twisted something......
I'm still learning, but this is NOT-a-panic-situation, so don't rush to your local sandbox and risk injury
or sliding up and down your RL roof taking measurements 
Here's my setup:
- Making a roof section with a Cube 1mx1mx1m,
- Hollowed
- Path Cut 0 to .5
- Rotate X=0, Y=270, Z=45
Now, Shift Copy, and rotate the resulting duplicate 90-degrees in Z-axis
Reposition so you now have lowest edges of the two roof sections touching.
Now, nudge the edges together,
You are now missing the "PEAK" where the two sections intersect. So it's kinda a 45-degree cut.
IM me in world if this is toooooo cryptic

