When using the map, you can add walls by selecting the pencil on the left-hand side. Here you can choose the type of materials that closest match your scenario (you can even adjust the wall thickness and height).
When a material is selected, click and drag to draw the walls onto your image/map. You can adjust the walls once drawn by clicking the blue nodes. To delete a wall, you simply right click the wall and press the Delete button on your keyboard.
Once the environment is outlined and virtualised, you will just need to set the set the map scale to add the units. You can find the instructions for this next step on our article UniFi - Controller: Adding devices to the Map.