Instructions from Video:
Creating a porch roof can be as easy as stretching the edge out of an existing roof to cover your porch or as simple as adjusting the roof type to be a double slope.
Let’s look at both options:
Stretching roof edge
Left-click to select the edge of the roof that you want to stretch out over a porch area. When you select the roof edge arrows will appear along the edge of the roof on each separate roof surface. The side of the roof you selected will have a green arrow, indicating it is ready to be edited. At the end of the arrow is a blue grip. A grip point will allow you to pick up the roof from that point, where the roof is currently supported, and move it to another support area. Put your cursor on the blue grip and holding down your left mouse button and keeping it depressed move the edge of the roof to a new position, release the mouse button when you have it in the new spot. That same slope will now carry down to your new support point.
If you want to have two different slopes, one over the porch area and then connecting into a different slope for the main house;
Double slope option
Select the roof edge that you stretched out to the new support point. Right-click and select Properties.
In the Roofs dialog box, select the Roof Shape button. Change the Roof Shape to Double. There are now 2 surfaces listed under Roof Segments. Surface 1 is the surface at the support point. We can define a slope and horizontal distance we want for this slope. Change the a-Slope Value to 3. To make the porch roof a 3 in 12 slope roof. Change the f-Horiz. Distance to 5′. To make the 3 in 12 roof cover 5′ horizontally of the roof. This will change the e- Fascia Distance. Set it to 8′ to match the main roof. Select Surface 2 from the Roof Segments list. Set the a- Slope Value to 6 to match the main roof slope of 6 in 12. Click OK and the roof is redefined with the double slope.