A building system for fabricating a multi-storey building structure, the system comprising at least one first building structure and at least one second building structure and a way for elevating the second building structure to allow provision of the first building structure under the elevated building structure. A method for fabricating a multi-storey building structure, the method comprises the steps of providing a second building structure; elevating the second building structure; providing a first building structure under the elevated second building structure; and lowering the second building structure onto the first building structure. There is also provided the elevating means, such as jacks for elevating the building structure.