Preheat oven to 400°F. Grease the bottom and sides of a 9x13 inch casserole dish. Start cooking macaroni according to package instructions. You may start to brown the sausage remember to stir frequently to keep from burning.
While these are cooking, place flour and margarine in a 6-cup measuring cup or equal size mixing bowl. Place in microwave on high for 30-45 seconds or until margarine is fully melted. Remove and stir. Add milk and put back in microwave, on high, for 2 minutes. Stir again and add 2 cups cheese. Put in microwave on high for 3 minutes and stir. Drain macaroni and drain sausage. Mix all together in the 9x13 dish. Sprinkle with 1/4 cup cheese.