To draw a simple pitched roof, draw a line in the middle of the roof area and drag it to the desired height.

Steps

Select the Lines tool in the Getting started bar.

Alternativly press [L].
Move the cursor to the short side midpoint.
The midpoint is catched automatically.
Left-Click once.
Move the cursor to the opposite side.
Left-Click once.
The center line is displayed in black.
Select the Move tool in the Getting started bar.

Alternativly press [M].
Move the cursor to the center line.
The center line is displayed in blue.
Click the center line and drag the cursor up.
The center line is attached to the cursor and can be moved upwards.
Take care to move the cursor parallel to the blue axis, as in the following figure.
Set the roof height and press [Enter].
Simply type the value using the keyboard, e. g. 5,5.

Result

You created a pitched roof in the desired height.
To draw a pent roof, pull the corresponding outer edge upwards.