There are a lot of different designs he can choose from. Here are a couple from a search.
https://duckduckgo.com/?t=ffab&q=a+frame+portable+chicken+run&iax=images&ia=images
If you want it to be predator proof you will want to use 1/2" hardware cloth and have 18" of the same on the ground...
It is all about your situation. You just have to weigh everything and make the best choice for what you have going on, I think. I was letting out 7 week old chicks, but they had an older flock that they were going along with, so the different variables change things.
Maybe you can set up something like this, or something similar that serves the same purpose?
Or they can be out when you are out as well? They are very vulnerable at that age.
I usually herd with food or treats, but that young they may get confused. They will want to go back to their domicile...