The system has underframe elements (6) with adjustable height, and a grating formed of grating elements (18) and closely placed on the underframe elements. The grating supports square shaped modular trays, where each tray comprise polygonal bottom pierced with calibrated holes i.e. openings (28) and lateral sides (34). A reversible fitting unit is formed with a groove (36) and a rib (38) and arranged on the lateral sides of the trays for fitting the modular trays. The underframe elements are provided with a planarity adjustment unit i.e. ball (16). An independent claim is also included for a method for covering a sealed roof with plant cover.
