A set for forming a functional area in the form of a reflector surface of a luminaire, an air passage, an opening for a sanitary installation, an outlet of a heating system and/or of a cooling system, in a component made of a castable and curable building material, in particular in a concrete ceiling and/or a concrete wall, comprising: a) a mounting aid which can be loosely attached to a mould or a formwork for the castable and curable building material; b) a formwork insert which, on an outer side facing the castable and curable building material, has a shape substantially complementary to the shape of the functional area to be produced; c) a mounting body, which can be loosely attached to the mounting aid and is intended for installation in the component made of the castable and curable building material; d) a pressing device (7, 9) which enables the formwork insert to be pressed against the mould or the formwork when the formwork insert is placed on the mould or formwork; wherein the mounting body comprises a pipe section open on both sides or a sleeve open on both sides, wherein the set further comprises an insert element which, at least in certain areas, in particular substantially completely, has a shape complementary to the formwork insert and/or to the functional area to be produced, and the insert element preferably being designed in such a way that it can be connected to the mounting body, characterized in that the formwork insert is designed as a curved disc, the outside of which is convexly curved, and in that the insert element has essentially the same outer diameter, the same outer diameter, the same shape and/or the same size as the formwork insert and the insert element has the shape of a curved disc, and wherein the insert element is a reflector element made of a metal, wood and/or a polymeric material. a) a mounting aid which can be loosely attached to a mould or a formwork for the castable and curable building material; b) a formwork insert which, on an outer side facing the castable and curable building material, has a shape substantially complementary to the shape of the functional area to be produced; c) a mounting body, which can be loosely attached to the mounting aid and is intended for installation in the component made of the castable and curable building material; d) a pressing device (7, 9) which enables the formwork insert to be pressed against the mould or the formwork when the formwork insert is placed on the mould or formwork; wherein the mounting body comprises a pipe section open on both sides or a sleeve open on both sides, wherein the set further comprises an insert element which, at least in certain areas, in particular substantially completely, has a shape complementary to the formwork insert and/or to the functional area to be produced, and the insert element preferably being designed in such a way that it can be connected to the mounting body, characterized in that the formwork insert is designed as a curved disc, the outside of which is convexly curved, and in that the insert element has essentially the same outer diameter, the same outer diameter, the same shape and/or the same size as the formwork insert and the insert element has the shape of a curved disc, and wherein the insert element is a reflector element made of a metal, wood and/or a polymeric material.