Two new ideas:
Glass roofs and tiling so you could create greenhouses
Those green plants you see on the side of buildings...
Something like this maybe? Just a little more green.
MORE WINDOW TYPES! And a window designer and height modifier. And more options on staircases such as easy L's, U's and total square ones. (4 levels). And a way to delete the circular thing on spiral staircases so it isn't a circle it's a square on the floor above.