It would help if we saw a picture of your house to get an idea of what you have to work with, ie; decks, balconies, etc.....
I have an older (Circa 1898) house that is two stories. We built a deck off the front of the house that was perfect for converting into a pirate ship. Here are some pics of my ship when I first started building it:
This is what it looked like when it was all done:
Let us know what you were thinking of building and I am sure you will get lots of help and advice from the members here on the board.......The folks on this forum are great.....

!!!!