To do it right you'd have to build the structure with reinforced concrete, able to withstand tonnes of soil while forming a desired shape. You can then decorate

To do it right you'd have to build the structure with reinforced concrete, able to withstand tonnes of soil while forming a desired shape. You can then decorate it from inside as you want, make an exact copy of Bilbo's house if that's your goal. Such a project would be quite expensive though and well beyond capacity of an amateur.