Any room in the house may be turned into a dedicated leopard habitat simply by installing a leopard.
Carpet your bedroom floor with old socks.
If your roof leaks, put an inflatable swimming pool under the leak to create a Roman-style impluvium.
Turn a spare bedroom into an office by posting a sign on the door that says “office.”
Purchase books of uniform size and thickness, and use stacks of them to build shelves for the books you actually read.
Instead of laboriously installing a doggie door, simply leave the back door open. You will achieve the same result with far less trouble and expense.
If you have artistic talent, painting a trompe-l’oeil sunroom on the back of your house is a great deal cheaper than building one.
If your kitchen and dining room are on separate levels, a llama is much easier to install than a dumb-waiter.
To add hundreds of thousands of dollars to the value of your house, move it to a better neighborhood when no one is looking.