After the porch roof and main front roof is on, you can go ahead and install the back roof. Use a mallet to get tabs into slots and then masking tape to hold everything together until dry.
You then have to install the front gable roof roof.
Now this roof is a little tricky because you don't really know where the wallpaper will fall in the interior until the roof is on so you might want to patch any prints that might fall into the wrong room as you assemble. Do one side first and check your wallpaper and then do the other.
Make sure it's straight and flush. Clamp to dry.
You should install the front door side windows, exterior trim at this time as well.