How much Health do I need for roaming?
Mara is much more superior compared to valk
http://www.twitch.tv/sindrenerr
anything above 15k is adequate.
gw1 – healing signet/frenzy/charge
I go anywhere from 16k to 19k. Mara is a great choice, I personally use Mara/Soldier/some other stats.
https://www.youtube.com/channel/UCK3wy8xit2wonN7LouDJQ3w
http://www.twitch.tv/havocgw2
The amount of health needed is related directly to how much condition cleanse you carry, coupled with access to dodges and stealth along with your ability to use the same in game.
As with any of condition cleanses, vitality , toughness and dodges I really do not rely on the consensus of others. What I do is overkill in as many of these as possible and then scale back to a number I find comfortable with my own playstyle.
Added to that the weapons you choose factor in as well. As example If I am using SB off hand for mobility than why not use Sentenils SB? You are not relying on it for a lot of damage and just swapping to it can add to your health in a pinch and mean the difference between a safe exit or being downed.
I use mara weps, valk armor, bers/valk trinkets with a berserker ammy. Gets me very nice stats.
once thief hit around 17k hp pool in WvW you basically become unkillable assuming you know all match up.