My husband built one of these for our feral cat "Ghost Cat". He, and the other strays, have used it every winter and on rainy days. It is easy to make and they seem to like it. Outdoor cat house shelter for outdoor cats
Winterhaus für Streunerkatzen:How to build a feral cat shelter. The Humane Society suggests placing two shelters with their doorways facing each other and securing a board between them to create a canopy.