The CSM Stray Foundation Winter Shelter
Here's an idea inspired by the CSM Stray Foundation in Kew Gardens, Queens:
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 utility knife, and straw, shredded newspaper or other insulating material. Then assemble as follows:
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.
Line the floor of the bin with a piece of Styrofoam, using the yardstick and box cutter to cut out the piece.
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.
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.
Stuff the bottom of the bin with straw or other insulating material to hold the Styrofoam interior wall pieces in place.
Cut out a Styrofoam "roof" to rest on top of the Styrofoam interior wall pieces
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. Catnip can be sprinkled inside at first to attract the cats.
The Styrofoam Cooler Shelter
An adequate shelter for one cat can be made from a simple Styrofoam cooler available at any hardware store. 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 five to six inch round hole towards the left or right of one of the long sides. The attached lid will allow for easy cleaning.
Adding Mylar for Warmth
Mylar blankets are also effective when laid on the floor of the shelter or used to line the walls of a styrofoam shelter. They don't absorb and take away body heat like ordinary blankets when a cat lies on top, but instead reflect heat back. That's why they're sold as emergency blankets for car travel in wintertime. Mylar blankets can be purchased at a cost of $1.50 each from Healthy Harvest.
Go to http://www.healthyharvest.com and do a search for "Mylar Blanket."