Okay, cool things. Let's start with a big tree house. It's cool.
I'm sure you know how to build a tree.... If you don't, you may need some help..
You could also make a glass tower, just make it like steps going out and then going it to make a square-like structure
I also got to making a maze, though it takes time. But people will want to try it when it's finished!
I think this is cool too! Make a statue of yourself! I made this and you can actually go inside and look out of the eyes!
Lastly, just be creative and make several houses that would fit into the dream house category of yours..