Road 10 to 11 speed upgrade, what needs to change? Hope all is well.
Currently I have a Cervelo P2 2013 with an Ultegra 10 speed.
I would like to upgrade the drive train from the current 10 speed to an 11 speed setup (either the 105 or the Ultegra). The main question that I have is how do I know which bottom bracket do I need to get for the 11 speed setup to work correctly? Apparently it has a FSA Gossamer Mega Exo bottom bracket currently.
Is there anything else that I would need to consider besides the below:

cassette
derailleurs (front and back)
chain rings
chain
TT gear levers

The current brakes that are on the bike feel fine so I don't need to change those and I have 11 speed compatible rims (Campag Zonda's).
http://www.bikeroar.com/products/cervelo/p2-ultegra-2013/specs
I've done this conversion last year on my #2 bike from a 2013 Ultegra 10-speed to a 105 11-speed, to be able to use the 11-speed equipped wheels of a newer bike on my two bikes alternatively and avoid cassette swaps to do so.
The swapped parts are: the brifters, both derailleurs and the chain. The cassette of course! There is no need to replace the chainrings, the inner width of 10 and 11-speed chains being the same. It is only the outer width that changes because 11-speed has thinner plates. You could also keep the FD but I've chosen the new 105 FD. It is sleeker and easier to set-up and fine tune.
The quality of 105 from the most recent edition is far above Ultegra from '13, due to trickle down of technology. The most expensive part being the brifters.