Use the polygon tool to get the area of any room, object or building no matter what shape it is.
Check out this 40 second video or read how to below, 

To use it:

- Select the 'polygon' tool,

- Click 'New Group'
- pick a colour & name the group
- Click on a point to start the line.
- Click on each corner of the area,
- Double click to finish the measurement.