Here is a kitty hideaway that gives your feline friends a place to hide and relax outside. The Palram Mona Outdoor Cat House has double entrances and a see-through wall to allow your cats to keep an eye on their surroundings. You can fit a standard heating pad in this.
This cat house measures 21.7 x 20.35 x 23.7″ on the outside. It has 8.9″ x 7.9″ flap doors. You can find out more about it here.