Preheat oven to 400°F. Place a cookie sheet upside down in the oven on a rack.
In a bowl, combine the shredded rotisserie chicken and Buffalo wing sauce. Mix well.
To assemble: Spread each tortilla with 2 tbsp. ranch dressing. Top the dressing with 1 cup chicken mixture, ¼ cup mozzarella, ¼ cup blue cheese, 2 tbsp. red onions, and 2 tbsp. celery. Repeat.
Carefully place the pizzas on the hot cookie sheet in the oven. Bake the pizzas until the cheese has melted and the edges of the tortillas are golden brown, 7-10 minutes. Once baked, remove from oven, cut the pizzas into wedges and serve.