Wall length, without the walls?

[Takuto_90]

Hello.
How can I input the length of a wall and make it so that the inside of the walls aren't taken into consideration? When I measure an actual wall is from the inside, but when I punch in the length it subtract half the walls-inside measure. I don't want to have to have to add the 15cm of my walls in the measure, if that makes sense.
Maybe there's already a setting for it, but I couldn't find it.
Thank you very much in advance.

[Puybaret]

Watch this video.

[Takuto_90]

That was genius!! [=D>] It never occurred to me that I could draw the floor first and the then add the walls around! Also the video has some useful tips on measuring after the walls are done!
Thank you!!