I upgraded to a 50x15 blower part cooling fan, and tried to use the official Printrbot blower fan shroud, but did not like how it blew straight at the hotend top, which made my hotend not able to keep a stable temperature when the heat bed was heating.
I took the Printrbot version and added a downslope, and also tweaked the mount to work better with the 50x15 blower fan that I purchased.
The fan shroud was not centered and too low, so I also tweaked to get it more centered and the bottom a little higher.
I also added a frame to make it easier to keep the shroud square to the fan output, since there is a little bit of play that messes up the angle.
There are three different shrouds - the difference is how much curve there is for the top of the output, to give more or less clearance to the hotend as needed.