Sorry for the delay...but Jen's Parents have been visiting with us.
I used 3/4" Medium Density Fiberboard(MDF) for most of the constructions, 3/4" Birch plywood for the drawer front and 1/2" plywood for the drawer bottom. I routed 3/4" out the drawer sides to make hardwood drawer tracks, to keep the drawer aligned, but they are not needed. I used these materials because I had them lying around. For screws I used #6 - 1 1/4" drywall screws. Make sure to get a matching counter sink, drill bit ($3 ish) This will enable you to fit the screw heads flush and prevent you from tearing out the materials. Home Depot and Lowes would be able to cut the materials for you, so don't panic!
List:
Box
2 - 3/4"x 33.5"x 11.5" (Sides)
2 - 3/4"x 33.5"x 21.5" (Top & Bottom)
1 - 3/4"x 20"x 11.5" (Back)
Fit everything together first, to make sure they fit flush. once they do, pre-drill all your holes first. MDF has a tendency to tear out. I glued, then screwed the sides to the bottom first and then set the top on and then inserted the back and then glued/screwed them all into place.
Drawer
2 - 3/4"x 32"x 6" (Drawer Sides)
2 - 3/4"x 18 3/8"x 6" (Drawer Font & Back) The reason it is 18 3/8" and not 18.5" is because you will need some room for the drawer to slide. If it were exactly 18.5" it might not slide properly.
1 - 1/2"x 32"x 19 7/8" plywood (Drawer Bottom)
1 - 3/4"x 21.5"x 13" Birch plywood (Drawer Face)
I fit the drawer front and back, flush, inside the drawer sides, pre-drilled them and then screwed them together. I then attached the bottom the same way, making sure that the drawer fit flush and square to the bottom. I then inserted the drawer to the box and attached the drawer front with some screws about 3- 4" up from the bottom and attached the handle. I them surrounded the whole thing in carpet.
Get a PDF of the drawing here:
http://www.hudson2001.com/tom/projects/litterrobot/diagram.pdf
L/R cutting instructions to follow.........