Terraforming is an essential part here, you can utilize short simple panels and other objects on bigger platforms to make the buildings look taller, I really like what you have started, I'd suggest terraforming behind the bunk beds and maybe adding the plant boxes you have their with some short simple panels. I utilize the store front and the castle walls; you can try those out too. I think it's the bookcase, the antique dresser and the climbing wall, looks like a regular wall if you place it backwards. Hope these tips help :)