I had seen commercial indoor dog "potties" that consisted of some sort of tray/pan, with either some kind of mesh floor or artificial turf, that were designed to allow your dog to relieve himself indoors. The mesh floor or artificial turf provides a pourous substrate to allows your pet to keep his/her feet dry, and the tray/pan collects the urine underneath. However, most had significant (at least from my point of view) price tags, considering the simple technology behind such a product. I knew I could duplicate this general idea, but for a much reduced price tag.
A shallow "underbed" sort of plastic storage tub was a logical urine collection system, but I thought for several weeks about what might make a good "top" that was pourous enough to allow urine to flow through, but with small enough "holes" that my dog could walk comfortably on top and not catch his feet/toes/claws. I considered grid-like flourescent light diffusers that had approximately 3/4" square openings, but these seemed rather flimsy and lightweight for my nearly 20 pound dog. I considered commercially-available plastic kennel flooring ( see http://www.petamenities.com/kennel-flooring.htm ) that was designed for this purpose, but would have involved paying for shipping to my home.
Then, one day in the bread section of the local grocery store, I saw a product that would work VERY well, was readily and locally available, and was both quite pourous and very strong: the sliding "trays" that fit into vertical wire "racks" that are used to transport bread and buns from the bakery to the grocery store. These are made of the same kind and grade of plastic as are plastic milk crates, and are perforated with numerous small diamond shaped holes that are small enough to allow my dog to walk on the surface but allow urine to flow through into a plastic tub below. Being made of plastic, such a tray would be easily trimmable to fit the size of my plastic tub below. Such trays are standard sized to fit into the wire "racks" used on the bakery trucks and are approximately 24.5" X 24.5" square.
I went to my local bakery and simply asked if they had a damaged rack - they gave me one without further question (if it was damaged, I couldn't see it; but I noticed that it was from a different bakery company).
Step 1: Building the indoor dog toilet
This step is pretty simple. You want to cover up the shallow plastic storage tub you use with as much of the plastic bread rack tray as you need. You won't be needing the lid of the plastic storage tub.
Since bread rack trays (at least in this area) are 24.5" X 24.5" square, I was lucky enough to find a plastic storage tub (designed to slide under a bed) that was approximately 24" long by approximately 16 1/2" wide by 4" deep.
Since you don't want your dog to relieve him/herself on any part of the mesh rack except over the tub that will collect the urine underneath, you'll want to cut the plastic bread rack tray so that it fits over the plastic storage tub below.
Using a Dremel (rotary) cutter, I trimmed approximately 7" off one side of the bread rack tray so that it would slightly overhang the edge of the plastic storage tub. The remainder of the bread rack tray fit perfectly over the plastic storage tub.
Step 2: Preparing your dog toilet for use
Many pet stores will sell you a liquid product designed to smell like dog urine that you can use to encourage your dog to urinate in a specific spot, but if you're not squeamish, you can save your money and duplicate this product yourself.
When you walk your dog to relieve him/herself outside, take a few paper towels, a rag or some other absorbent material with you. When s/he raises his/her leg or squats to urinate, stick your towel or rag underneath into the urine stream and get it as wet as you can. Bring that back to your indoor dog toilet and put that into the plastic storage tub and underneath the plastic grate you made from the bakery rack tray.
If you want the dog to defecate on the dog toilet, similarly collect a small amount of your dog's feces and also place it underneath the plastic grate you made from the bakery rack tray.
Since dogs decide where they want to relieve themselves based on scent and habit, you now have plenty of incentive to encourage your dog to use your indoor dog toilet.
Step 3: Training your dog to use the indoor dog toilet
I accomplished this goal as outlined below. Depending on your dog's and your personal situation, you will likely have to modify these ideas to fit your own needs and resources.
I was lucky enough to find an inexpensive second dog crate (it came with no pan) - a larger crate for a larger dog, but also large enough to hold the entire indoor dog toilet, for sale on the local Craigslist. My dog's daily crate had two doors (one on the side and one on an end), so having these two crates provided me with options.
I removed the door from the larger crate (and set it aside - I used it later). Using cage mesh, the removed door and plastic cable ties, I reduced the size inside the larger crate to no more than the size of the indoor dog toilet. Upon entering the larger dog crate, my dog can ONLY access the indoor dog toilet.
I then slid the two dog crates together, and using plastic cable ties, secured them together so that my dog can walk from his "home" crate directly into the larger crate containing the indoor dog toilet.
Dog crate training works on the principle that dogs instinctively will not relieve themselves into a confined area they consider to be "home" (their den). What I have now provided is an area attached to, but separate from, my dog's "home" (den) where he can relieve himself.
It took a few days for him to get the idea, and I was a bit later getting home the first day he did so, but I will say that I was happy the first time I looked into the indoor dog toilet and saw that my dog had gotten the idea and urinated in the toilet as I had designed it. In the following weeks, he "got" the idea better and now uses the indoor dog toilet when he needs to. I now leave the door to his crate open, and there have been times he has "considered" using the indoor dog toilet as an alternative to braving the winter weather to go outside. Obviously he has gotten the idea.
For more ideas on teaching your dog to use an indoor dog toilet, see http://dogs.lovetoknow.com/wiki/How_to_Litter_Box_Train_a_Dog , http://www.lovemypetsupply.com/doglitterbox.html , http://www.squidoo.com/dog_litter_training , or http://www.dailypuppy.com/articles/how-to-train-dogs-to-use-a-litter-box/03a36a22-2a3d-7314-43fc-1910327fceb5 ,