I would build the house first, you will have inspectors, etc... crawling all over your property. What I have encountered is that when you do something to your land that inspectors are unfamiliar with (or the county differs from the city) you will run into a mess of red tape and confusion, with the ultimate answer always being that you can't do what you want to do. After the house is done, and prying eyes are fewer, well, maybe you move some dirt around.
