Well you can get the caddy or B-line T bar fan box or you can get creative. I have done both. The Caddy boxes were over $25 the last time i used one and a special order item around here. I have used strut and allthread to drop down but man is it time consuming.
I saw one company use a 2x2 piece of 3/4" plywood with a pancake box as a fan support. That seems quick and easy but it definately did not give the proper support for a fan. And i'm sure it will look nasty in year or two after gravity takes its toll.
