This is my D3-FNC build for PvE.
It caps out the shield health at 2.35 Million HP and has 45% ADR as long as your shield is active.
The Ammo box has 15% skill haste included and as you just want to use it to heal your shield and blow it up instantly it actually comes back 15% faster than any other box making this one the best choice as a secondary skill. My Ammo box has a 19 second cooldown when I blow it up while standing in it giving me plenty of heal when I need it.
My weapons of choice are the House for obvious DPS reasons and the PP-19 as my "Tank everything and stay at full health" weapon.
It has a huge magazine and the self-preserved talent comes in handy when your teammates keep getting the kills and you just need a tiny bit of heal to leap over into the next segment to start regenerating to full health.
It can support your teammates with the Support station which you can simply blow up every 20 seconds. Just make sure you are close to someone else to let them benefit from the burst heal as well.
Played right this build can tank any mission in the game and even when you get flanked you can survive multiple punches from legendary NPC's.
Your toughness while sitting behind the shield will sit at around 1.2 Million base and once your D3 bonus gets proced you will jump up to more than 2 Million toughness. You are almost unkillable once that bonus hits.
In PvP you need at least 1 dedicated healer to keep your shield alive due to the overkill modifer on the PvP shield damage. (480% :/ )
Have fun and enjoy!