Bicycle Mechanics - Refacing a bottom bracket

I was wondering how this is done and how to tell if you need it done.

I'm going to be installing cranks with outboard bearings on a build I'm doing and wanted to make sure that everything was A-ok.

You need a bottom bracket facer tool. Its big bucks$$$$$$$$$$$$$ Normally I will face every new build that gets outboard bearings but i'm just anal about my bike builds. Unless you are going to be cutting shells weekly, i'd just go pay the lbs and get it done. And if you do it wrong, you can break the cutters, which is even more big bucks to replace them (the cutters are more than half of the whole set, the handles are rather cheap)

If you do think about getting a facer kit, don't cheap out. At the minimum get the Park BFS-1. But i'd recommend a VAR, Campy or possible a Cyclus set

Second taking it to your favorite LBS.

It's much more critical with x-brackets than older cartridge or cup 'n cone