Another handy thing is, you can demolish a PWP on the same day as building a new one. What you need to do is set up the PWP you want to build first, but not donate anything to it yet. Then you can go back into town hall and sit in your chair and talk to Isabelle about PWPs. Then pick the demolish option. You can knock down one PWP and once that's paid for (she takes the money as you're sitting in your chair), you can go back outside and pay the bells for your new PWP. That means the next day, you'll have a new PWP, and the old one will be gone. I find this really handy for when I'm doing some major re-landscaping!!!