First, you need to make 4 divider walls.  Glue 4 sets of half-tiles together back-to-back, and set them aside to dry.  Also cut your 2X2 plywood into four squares, each exactly the size of your floor tiles.

Materials needed for this step:
4- floor tiles (12"x12")
  8- floor half-tiles (6"x12")-have your hardward store cut the tiles in half for you.
1 tube of construction adhesive (to glue the half-tiles together)
Plywood (2'x2'x 1/2")- smooth face
 
 

Now, build the frame.  It will be a square equal to the length of 2 floor tiles, plus 4 times the thickness of your wall tiles.  It is built with two end pieces and 3 spreaders.

Materials needed for this step:
2- 6' long 2"x4" straight studs-clear
1.5" outdoor deck screws- for toenailing frame together
 
 
 

Set one of the plywood squares on the frame so that there is one tile thickness from each edge.  Secure the square with deck screws.
 
 
 
 
 
 
 
 

Using your double-thick tile walls as spacers, set the other plywood squares in place and secure with deck screws.
 
 
 
 
 
 
 
 

Set the tile walls into the grooves without glue.  Apply adhesive to the bottom of the floor tiles, and place them securely making certain they are tight against the divider tile walls.