Heat the oven to 425 degrees Fahrenheit. Line a baking sheet with parchment paper, foil or a silicone baking mat. Cut cauliflower into florets, rinse and pat very dry. Add the florets to the baking sheet then toss with the oil, 1/2 teaspoon salt, and 1/4 teaspoon fresh ground pepper. Spread them out, facing as many of the flatter edges down onto the baking sheet so that they brown nicely. Roast, stirring after 15 minutes, until the edges are crisp and brown and the stems are tender, 20 to 25 minutes. When the cauliflower is almost done, make the buffalo sauce. Melt the butter in a small saucepan (or use a microwave). Slide the pan with melted butter off of the heat, and then whisk in the garlic powder and hot sauce. Toss the buffalo sauce with the roasted cauliflower, and then place back into the oven for 5 minutes. Serve immediately alongside celery and a creamy dipping sauce like ranch or blue cheese.