Use the Polyline Tool to draw the overall shape of the building.
Once the overall shape of the building is drawn, it needs to be Offset.
The first Offset line is drawn at 1200mm.
Copy the original Offset line and Offset the copies in 600mm increments. Offsetting at 600mm, then 1200mm, then 1800mm.
The Offset lines give the placements for Elevations, Sections and Dimensions.