A method includes the steps of: (a) wrapping a stack of composite prepregs around a plate-shaped mold core to obtain a bag-like preform; (b) removing the mold core from the preform so that a receiving space is left in the preform; (c) inserting an airbag into the receiving space; (d) placing the preform together with the airbag in a mold; (e) inflating the airbag and hot pressing the preform within the mold until the preform is cured so that the receiving space is formed into a motherboard receiving space with a size sufficient to receive a motherboard of the notebook computer and so that the preform is formed into a one-piece flat housing body for the base of the notebook computer; and (f) removing the flat housing body from the mold and the airbag.