In Roomle you can upload a background image of your floor plan with the exact measures and position of the walls in order to draw a more accurate plan.
Open a new plan and click on the 'Upload file' button and select your image.
Once your image is uploaded to your Roomle plan a ruler appears in the center of the planning area.
Scale up the image and use the ruler to set the correct proportions of your plan. In this way, when you draw a wall over the image, it will have the correct measurements.
When you are finished, click on the 'Apply' button. You can now start drawing the walls using the image for reference.
Note that during drawing walls (double click left mouse button) the floors are hidden to see the image in the background. The floors are shown as soon as you exit the drawing mode.
The image will come in the front of the plan - you can edit the proportions you set in the beginning and click on 'Apply' to save the changes. Or if your plan is complete, you can delete the image.
The image won't be visible in the 3d view.