Here you we be able to see how to add your own meshes to the wall tool and set there default values.
Once you have imported your own mesh open the mesh editor in the top left hand corner of the view port you will see approximate size you will need to make a note of these numbers, the numbers are the meshes size in the 3 axis in the order X Y Z.
Once you have these numbers noted down open the BP_WallTool and find these nodes. Here now replace the select node with the mesh half high bool connected false value with the Z number you noted down.
Next change the 100 x 100 value in the other select node to 1 less then your Y value (So if you Y value is 125 you need to enter 124).
Now replace the 100 x 100 value highlighted on the left with Your Y value, once thats done you can select the Wall 100 x 100 variable to your own mesh (This is optional but will mean the when you drop the tool in the world it will start using it without you having to change it in the details panel).
If when you drop the tool in to the world there is no meshes try dragging out the spline as the default spline length may be shorter then your mesh.