If you’re not a perfectionist, drawing plaid is simply a matter of opacity.
To draw the plaid on Tim’s blue shirt, I made his vertical plaid stripes white and 30% opaque. When the vertical stripes cross the 15% opaque horizontal stripes, the intersection is 45% opaque, giving it enough of a plaid look to please an Illustrator beginner like me.
I used similar opacity levels to add the dark red stripes. Now, how do you illustrate a face?