The slices need to be the material thickness multiplied by the scale if working at full size

e.g. 6mm x (1:)500 = 3000mm = 3m

or simply the material thickness if the model has been scaled.

Use the Contour command, select the objects to slice, pick the base level for the first slice and then the direction you want the slices to be stacked in (from an elevation view), then specify the distance followed by RETURN.

Other options are available in the command line, once the slices are created lay them out as required to fit the A1 or A2 laser cutters.