To start with I cut out all the pieces and assembled them as needed.
Note, the back wall that attaches to the smaller peak is slightly angled, not the straight edge.
Below is the large peaked house.
When assembled, this is how it should look flat.
Fold the smaller addition portion to the right.
When standing your house up, it starts to take form.
Start gluing the remaining tabs to make the box shape
This funny looking little piece will fill the void between the roof and the small front addition.
It is actually pretty simple to form. Fold the top tabs inwards
Then fold the remaining tab downwards
This is what the addition should look like!
Flip the roof over and glue the tabs in place
Next glue the front tab to the front of the roof, this is how you will attach the wall of the small addition (with the largest window) to the structure.