I've been playing the same save with the Goth/Crumplebottom family for close to 3 years now, and between moving them and their house from Sunset Valley to Moonlight Falls I've done a ton of renovations on their house and lot. I especially needed more space since I've had a mix of the Goths and Crumplebottoms living there. I've decorated a lot more since I took these and I think added/split some rooms.
4th floor and rooftop
Here's a few photos of what it looks like in the new rooms and the house from outside!
The Crumplebottom kids' room
Queenie Goth (granddaughter of Cornelia and Gunther) in one of the new bathrooms
The house from the front!
I'd love to see what others have done to premade houses.