Use the "Wall Tools" to draw a shell. The "Auto Dimension" tool instantly adds temporary dimensions.
If you own Chief Architect Premier X15, upgrading to X16 (v26.3.0.10) costs approximately (or is included with an active SSA – Software Subscription Agreement). chief architect premier x16 v263010 x64
X16 introduced the ability to import (from drone surveys). Version 26.3.0.10 improves the smoothing algorithm for terrain perimeter. Use the "Wall Tools" to draw a shell