You can find the create measure plane tool in the 3D viewer tool dropdown which is the third button on the top right of the 3D viewer.
Creating measure plane
You can create a measure plane by first selecting a surface, for instance a wall. Then right-click and select "Create measure plane". The model will then be clipped by a measure plane that we can only see the outline of and parallel to the surface we have chosen when we added the measure plane.
Creating a measure plane from a clipping plane
In the bottom left of the model viewer you can choose between the clipping planes. By left clicking on the plane you want. The plane will by outlined with green.
With the plane selected you can drag to adjust it to where you want your measure plane to be.
You will then see a measure option on the bottom left which you can choose to create a measure plane from the clipping plane.
Closing a measure plane
If you have activated a measure plane you will see a close button on the top left which you can click to leave the measure plane.