With the "Vault" command, the section drawn with two-dimensional tools is defined to the vault to form, and the vault form is created.
The steps you should follow are;
Draw the form of the vault section in the drawing area using the line, arc or curve commands.
Click the Roof/Vault command.
Select the lines, arc or curve you have drawn to determine the section form by clicking with the left mouse button in the drawing area.
Click the right mouse button the cursor will change.
Click on the drawing area with the left mouse button. The clicked point will be the starting point of the vault.
Drag the mouse cursor. The vault will stretch with the mouse cursor. By pressing the space-bar key on the keyboard, you can have the vault defined at the bottom, top or middle.
Click the left button again to select the second point of the vault. The vault will be drawn.