I've tried to draw the plan with dia, gimp and inkscape, but that was too dificult for me. Is there better drawing tool for that?
Ubuntu – Drawing tool for evacuation plan
software-recommendation
Related Solutions
Warning: broken. Shutter is severely broken in Ubuntu 18.04 and not available in later versions.
Shutter (which you can install from the Ubuntu Software Centre or sudo apt-get install shutter) is a tool which has a variety of options for taking and annotating screenshots. (Note: You can annotate any images of your choice, not just screenshots.)
Sweet Home 3D 
Sweet Home 3D is a free interior design application that helps you place your furniture on a house 2D plan, with a 3D preview.
Best Answer
Try OpenOffice/LibreOffice Draw. It is installed by default, in the Graphics menu.