An installation system comprising a roof window, a lining panel and a plurality of bracket members for providing connection between the roof window and the lining panel, the bracket members comprising at least a main portion having a first fastening zone configured to be connected to the lining panel and a border portion having a second fastening zone configured to be connected to the roof window, characterised in that the installation system comprises existing packaging of other parts than the bracket base members in a supply condition, the plurality of bracket members are substantially plane bracket base members with a predefined width and height comprising at least one first set of longitudinal weakened portions (31, 41) to provide a first longitudinal folding line and at least one set of transverse weakened portions to provide a transverse folding line extending at right angles to the first longitudinal folding line and dividing the bracket base member into at least two sections (10A, 20A), at least a first bracket part and a second bracket part are configured to be formed by the respective sections (10A, 20A), and the main portion (11A; 21A) of the respective section (10A, 20A) is formed on one side of the first longitudinal folding line and the border portion (12A, 22A) on the other side of the first longitudinal folding line, wherein a first plurality of bracket members are configured to be formed as corner brackets in which a second section of each bracket base member has been bent substantially 90° about the transverse folding line relative to a first section, and each section (10A, 20A) of the respective bracket member has been bent substantially 90° about the first longitudinal folding line to form the border portion (12A, 22A) to extend substantially perpendicularly to the respective main portion (11A, 21A) of the bracket section (10A, 20A), said corner brackets being connectable to corners of the roof window and of the lining panel, and a second plurality of bracket members are configured to be formed by separation of a first section from a second section of each bracket base member along the transverse folding line to form at least two bracket parts (101, 102, 104) of a single bracket base member, and each bracket part (101, 102, 104) has been bent substantially 90° about the first longitudinal folding line to form the border portion (12A, 22A) extending substantially perpendicularly to the respective main portion (11A, 21A) of the bracket part (101, 102, 104), said bracket parts (101, 102, 104) being connectable to sides, top and bottom of the roof window and the lining panel, and that the plurality of bracket base members are fit into said existing packaging. the installation system comprises existing packaging of other parts than the bracket base members in a supply condition, the plurality of bracket members are substantially plane bracket base members with a predefined width and height comprising at least one first set of longitudinal weakened portions (31, 41) to provide a first longitudinal folding line and at least one set of transverse weakened portions to provide a transverse folding line extending at right angles to the first longitudinal folding line and dividing the bracket base member into at least two sections (10A, 20A), at least a first bracket part and a second bracket part are configured to be formed by the respective sections (10A, 20A), and the main portion (11A; 21A) of the respective section (10A, 20A) is formed on one side of the first longitudinal folding line and the border portion (12A, 22A) on the other side of the first longitudinal folding line, wherein a first plurality of bracket members are configured to be formed as corner brackets in which a second section of each bracket base member has been bent substantially 90° about the transverse folding line relative to a first section, and each section (10A, 20A) of the respective bracket member has been bent substantially 90° about the first longitudinal folding line to form the border portion (12A, 22A) to extend substantially perpendicularly to the respective main portion (11A, 21A) of the bracket section (10A, 20A), said corner brackets being connectable to corners of the roof window and of the lining panel, and a second plurality of bracket members are configured to be formed by separation of a first section from a second section of each bracket base member along the transverse folding line to form at least two bracket parts (101, 102, 104) of a single bracket base member, and each bracket part (101, 102, 104) has been bent substantially 90° about the first longitudinal folding line to form the border portion (12A, 22A) extending substantially perpendicularly to the respective main portion (11A, 21A) of the bracket part (101, 102, 104), said bracket parts (101, 102, 104) being connectable to sides, top and bottom of the roof window and the lining panel, and that the plurality of bracket base members are fit into said existing packaging.