I've looked into doing this also and here's what I've discovered after talking to some of the shelters.
They would be looking for mats to line the crates so I would suggest if you want to sell them for extra money, you could make mats (will explain in a second).....that would fit the 3 typical sizes of dog crates (or cat crates which would be smaller). Here's a link to a popular site for pet needs showing the type of bed mat I'm talking about.
http://www.drsfostersmith.com/dog-su...pid=PPC-G-3928
As for making the mat, you can stuff it with a foam pad at least 2" thick or polyfill. I've used fabric scraps for beds for my spoiled doxie but that makes them quite heavy .... then tie like a tied quilt to help from shifting. I found this tied process not easy without a good, long upholstery needle.
Good Luck in your venture!!!