The present relates to a device being used in modular building construction comprising at least one flat load support comprising a first main face and a second main face, at least one elongated load support designed for being coupled with said flat load support. The device is characterized in that said flat load support comprises an array of transverse openings extending through the thickness of the flat load support. The flat load support is arranged for fastening said flat load support with said elongated load support at any position corresponding to one of said opening in a reversible manner and to any position between said openings in a reversible manner. Each flat load support comprises reversible lateral connection means and/or reversible transversal connection means for coupling flat load supports in a reversible manner. The flat load support and the elongated load support are arranged for being detachably assembled to provide the modular, reversible, and/or versatile building construction. The invention further relates to a modular construction building based on said device and to a method using said device.