Make square- or V-shaped notches on the edges of your plastic or wooden flat surface. This will allow you to "comb" the adhesive on the tiles.
Glue the handle to the middle of the flat sheet of wood or plastic. Your glue must be heavy-duty and not house glue.
Let your trowel sit for a day, so that the glue dries thoroughly. Forcefully drag it across a surface to test its durability. Remember that you are going to apply the adhesive to the floor using your trowel. If your handle comes off, you will need to make a better trowel.