Why is there a separate "building site" board? Why isn't this just printed on the main board? Please tell me there's a good reason to make it so everything on the board can be knocked all over the place if the building site board is bumped.
Because with a fixed board you would not be able to change the layout. According to the rules may the building board be placed anywhere within the central area of the large board - as long as it doesn't cover any of the villages.