The Michigan Department of Transportation (MDOT) has set up a website dedicated to helping folks get down to Ford Field for the Final Four this weekend. They've broken down the directions for people traveling from north, south, east, and west. There is also a PDF for each section (north, south, etc.) that you can download and/or print out for your trip. You can access this special page here.
Also of note:
The Michigan Department of Transportation (MDOT) reminds fans heading to Detroit for Final Four events that the closure of northbound and southbound I-75 between Clark Street (Exit 47A) and the I-96 split (Exit 48) near the Ambassador Bridge will affect your drive.
Drive safe and Go Spartans!