They could come up with a size from the IRC. However, we do not know what they are building. How many floors, what is the support, what is the exterior bracing, and what is above.....and what code they are following in their location.
With an engineer for 400 bucks , they get a correct answer instead of lots of guesswork, and the nifty piece of paper for the building official.
Let us know what you end up with, these projects are fun to watch.