A good alfredo is simple, butter, cream and cheese. I know one italian restaurant owner that starts with a roux, but that's mostly so it keeps better. He always catered to the lunch crowd. It was still good, but not great. I've often considered experimenting with a roux to cut down on calories, but never have.
Anyway, Here's mine:
12 oz pasta
8 oz butter
2 cups heavy whipping cream
1 1/2 cups grated parmesan cheese (not shredded, but grated).
Melt the butter in a heavy frying pan over high heat, until the butter begins to brown. This adds a tint to the cream and is important IMO. Add 2/3 cups cream and reduce.
Remove from the heat add the cooked pasta, 2/3 cups cream and 1/2 of the cheese. Mix and repeat with the remaining pasta and cream. Serve immediately.