Make buffalo sauce: In a small bowl, whisk together melted butter, hot sauce, and garlic powder and season with salt and pepper.
Reserve 1/4 cup for serving, then drizzle remaining buffalo sauce over cauliflower and brush evenly to coat.
Roast until cauliflower is golden and tender, about 1 hour 25 minutes. Check regularly is it is starting to burn remove and turn the oven down.
Drizzle roasted cauliflower with ranch dressing and reserved buffalo sauce and sprinkle with blue cheese, diced celery, and chives.