Step 1. Draw some ADT (ACA) walls with rounded and straight walls.
Step 2. For the Roof: draw rounded (arc) lines and make this into a polyline with the function ‘Pedit’.
Step 3. Place the Polyline above the walls.
Step 4. Extrude the polyline with the command ‘Extrude’ over your building.
Step 5. Project the Walls to the extruded polyline, this has changed to a 3D Solid.
Step 6. Select all walls, right click and select Roof/Floor line – Modify Roof line, type A (Auto project) and select the 3D solid Roof.
This will project all your walls to the so called roofline.