I first assembled the base. Make sure that the good side of the wood is facing up on your first floor. As always, tacky glue first and then wood glue into all the joints.
Clamp tightly with masking tape.
After the base was done, I assembled the walls and the second floor. Very easy.
The box photo of the dollhouse seems to have a little inconsistency between the exterior and interior photographs. I think that the interior photo shows the dollhouse with the dutch door as the front door. To avoid confusion, just build as the exterior photo shows.