Where house builders quote prices does this typically include the foundations, and assume flat ground? (I know this is a vague question)
You will have plans and building regs. Get the builder to price everything on the drawing/project. Anything that is not shown, paths, fencing, garden walls, patio etc, should be written into a separate contract
and priced accordingly. You will need to hire a building inspector to check the works as they proceed, he will need to stamp the building book. Do not deviate from the project plans as you will be fined, even for a minor infraction.
There are lots of pitfalls, so be careful.