Materials needed are: a large Rubbermaid storage bin, an eight foot by two foot sheet of one-inch thick hard Styrofoam, a yardstick, a box cutter or utity knife, and straw, shredded newspaper or other insulating material. Then assemble as follows:
1. Cut a doorway six inches by six inches in one of the long sides of the storage bin towards the corner. To prevent flooding, cut the opening so that the bottom of the doorway is several inches above the ground.
2. Line the floor of the bin with a piece of Styrofoam, using the yardstick and box cutter to cut out the piece
3. In similar fashion, line each of the four interior walls of the bin with a piece of the Styrofoam. Perfect cuts are not necessary. Don't make the Styrofoam go all the way up to the top of the bin, but leave a uniform gap of at least three inches between the top of these Styrofoam "wall pieces" and the upper lip of the bin. There needs to be room for an interior Styrofoam "roof" to fit.
4. Cut out a doorway in the Styrofoam where it is lined up with the doorway that has been cut out already in the storage bin. Trace the outline of the doorway on the Styrofoam first before cutting.
5. Stuff the bottom of the bin with straw or other insulating material to hold the Styrofoam interior wall pieces in place.
6. Cut out a Styrofoam "roof" to rest on top of the Styrofoam interior wall pieces
7. Cover the bin with its lid.
This shelter can be cleaned by taking off the lid and the Styrofoam roof. It's also lightweight and may need to be weighed down. A flap over the doorway is optional. Catnide at first to attract the cats.
Spay and Stay, Inc., of Illinois, offers detailed plans and photos on its website for making inexpensive winter shelters from two Rubbermaid storage boxes: http://www.spayandstay.org/wintershelter.htm
Animalkind of Hudson County, NY, provides photos and instructions on its website for converting Styrofoam packing containers into cold weather shelter: http://www.all-creatures.org/ak/feral-shelter.html
An adequate shelter for one cat can be made from a simple Styrofoam cooler available at any hardware store for about $6. Glue the lid onto the cooler, turn it upside down and cut a hole in one side (anywhere but in the middle of one of the long sides). The Styrofoam containers used to ship meat can be turned into shelters in the same way and can, depending on their size, house 3 to 4 cats. If you want to get fancy, get a large Igloo cooler and, with a jigsaw, cut a hole towards the left or right of one of the long sides. The attached lid will allow for easy cleaning.
In a pinch for just a temporary fix, even a cardboard box is better than nothing - tape the top closed and cut out a hole in one side for a door. Tape a piece of plastic (cut out from a large trash bag) onto the top. Put newspaper on the bottom and, if possible, place the box under something to protect it further from rain -a piece of wood leaned against a fence, under a tree, etc. If possible, raise the box off the ground where it might get wet.
The cats' shelter will be warmer and cozier if you put loose insulating material inside. The material must be dry and loose, so that the cats can burrow into and underneath it. Straw is the best, while shredded newspaper will also work. The worst are blankets, towels or folded newspaper. Because the cats can only lie on top of these materials, they actually draw out body heat and defeat the purpose. But do keep in mind, if you use insulating materials, you must be able to change them regularly in order to ensure they stay dry. If you can't, it's better not to use anything except the shelter itself.
Claudia Allen of Winnipeg, Manitoba, Canada, lines the interior walls of her styrofoam shelters with a Mylar reflective blanket, which can be bought at survival stores as thermal safety blankets for people (in case your car gets stuck in the cold.) The Mylar reflects the cat's body heat back onto him and can make the difference in extreme temperatures, particularly in the more northern states and Canada. A detailed explanation of how to build Claudia's Mylar-lined winter shelter, complete with photos, can be found at: http://www.winnipeghumanesociety.ca/PDFs/reds_shelter_outdoor_cats.pdf
Claudia also uses an outdoor heating pad in the shelter and an electric dish that she reports keeps water from freezing as low as minus 38 degrees F. These items can be found at: http://cozywinters.com/shop/kh-3093.html (heating pad) and http://cozywinters.com/shop/kh-2010-2020.html (electric bowl)
Caretakers have reported the Mylar blankets are also effective when laid on the floor of the shelter. They don't absorb and take away body heat like ordinary blankets when a cat lies on top because the Mylar reflects the heat back.
Mylar blankets can be purchased at a cost of $1.49 each from Healthy Harvest. Go to http://www.healthyharvest.com/ and do a search for
Another blanket-type product reported to do a good job of warming cats in shelters is the "Flexi-Mat Mysterious Purr Pad." Made of polyester fibers, it absorbs then holds body heat. A set of two costs $9.99 and are available through PETsMART. The product is also available in a charcoal color for $10.99 for a set of two: