Preheat oven to 350 degrees. Cook macaroni according to directions and drain. Melt margarine in a large saucepan. Add flour and whisk together. Whisk in milk and cook over medium heat until mixture starts to bubble and thickens. Stir constantly. Add chunks of Velveeta and allow to melt. Salt and pepper to taste. Pour macaroni together with sausage and thawed broccoli into a 13x9 oblong baking dish. Pour sauce over top and gently mix. Bake in the oven for 20 minutes then put shredded cheese on top. Bake for another 5 minutes until cheese melts. Allow to cool for a few minutes before serving.