I do the roux thing at home, but for big cooks I use a big bag or two of elbow macaroni from SAMs with a #10 can of bakers and chefs cheddar cheese sauce from sams and a quart of milk. Makes two or three steam trays.
Boil the noodles, drain, add can of cheese, and some of the milk and mix. Thin with the milk until you get the consistency you want.
I preferr baked mac and cheese but the bakers and chefs cheese makes a ton of pretty decent mac and cheese for a good price.
I had a breaded and deep fried ball of mac and cheese with lunch today. Man was that good.