I notice a lot of people tend to take someone's "build" and then try to copy it but aren't able to achieve the same success. IMO you're setting yourself up for failure at the start with that mindset as your skills should be somewhat fluid depending on the situation and meta. The skills I use when I'm solo are not the same skills I use when I'm in a group of 3 people, and they're definitely not the same skills I use when I'm in a full raid. The skills I use today are probably not going to be the same exact skills I use in 2 weeks, and definitely won't be the same skills I use when IC drops in a month. I find if you're constantly making small tweaks to what you're currently using and trying new things out, you're in a far better position when the meta takes a hard shift, and far less likely to threaten uninstall and /ragequit when a nerf happens that affects your "build".

Stepping off the soapbox for a second, healers are valuable and dps is valuable (magicka or stamina) so long as you have enough survivability to synergize with your reaction time and playstyle. Tanks don't really accomplish very much other than being annoying, and the cyrodiil meta has almost always been about high burst damage and high burst heals. Very very rarely do you ever have engagements that last more than 20 seconds. I suppose tanks make good siegers? Smart (and average) players will quickly identify you as a tank and just ignore you until you're the last player alive because you're not really a threat compared to a dedicated healer or high dps player. If you're new to pvp and still getting the hang of things, going very defensive for a while so you can pick up on how things work can be a solid plan, but it shouldn't be your long-term plan. Unless you're a templar with rank 10 alliance war skill line and running a rez set, being a tank doesn't net you the same rewards as being a good dps or healer. I suppose if your group's playstyle is to always have someone drop a siege during every engagement, a survivable character would be best suited for that? Either way, if you're focused by a group, you're only going to last 1-8 seconds longer than a glass cannon in most cases.

As Bash-ley pointed out, unless you're a high dps build and plan on ganking, you should be running with a group (whether small or large) and base your objectives on your group size, as well as the skills you're using.