Adding a unit to your design follows the same principle as adding Wall items. Choose the layer you wish to add to (Base Units or Wall Units) then click on the required button. However, unlike with Walls, the buttons for adding units are arranged in several sub-menus. Return to top.dding a unit to your design follows the same principle as adding Wall items. Choose the layer you wish to add to (Base Units or Wall Units) then click on the required button. However, unlike with Walls, the buttons for adding units are arranged in several sub-menus. Return to top.