rattlecage is outdated and i wouldnt recommend it anyway, since the stats are meh....
gearing up on a magplar always depends on the weapons setup, meaning if you prefer dual wield, sword and shield or staves.
depending on that, there are a lot of possibilities, since there are sets like transmutatiion or wizards riposte, which only needs to be backbar slotted. both sets can be purchased at guildstores.
your gear setup also depends on what you are supposed to do in pvp. are you a healer or do you play rather a damage dealer? or are you even a solo player? depending on that, sets also vary a lot.
healers tend to use the supporting sets mentioned above with a crafted heavy armor set like shacklebreaker, kargenac's hope or seducer. Overall shacklebreaker is always a good choice.
going for some damage, war maiden or soulshine are very nice sets for magplars. for a bit more defence while casting jabs or jesus beam, cyrodiil's light also is a very nice option.
if you are a solo player, i strongly recommend desert rose for the magicka return you also have while being in mistform.
I enjoy the game a lot, but I am rather casual/solo in terms of playstyle. I'll group up in PvP but I have zero experience with VetDungeons. Therefore I have no Monster sets. Most current builds revolve around Zaan now currently, but realistically I won't have that.
I went with Soulshine (5) + Innate Axiom (5) + 3 Julianos to fill the slots.
I have one lucky Monster set shoulder piece which would give me +1096 Mag, so I am thinking to swap the Julianos for 2 Magnus + that shoulder piece for an additional 2100 Magicka. Once I make some cash again.
I don't know if Innate Axiom is any good with the +500 spell damage on class abilities, it seemed logical since I only use like 1 or 2 non-class abilities.
Yeah it will be a casual/solo PvP set up mainly focused on putting in a little damage. It's just to play PvP, learning the class in that scene while slowly gathering the more end-game things.
try to get hands on some more monsterset pieces, they really help a lot.
for some nice damage, the monsterset skoria fits magplars very well. if you use a dual wield and sword and shield setup, then you can go for a 5/5/2 setup, with two 5 pieces up all the time plus the monsterset.
since you crafted axiom (should be fine too, but still i think shacklebreaker would be better), i would go for warmaiden jewelry, gloves and sash, since the jewelry is arcane and gives you more max magicka, which increases your damage too.
soulshines jewelry is healthy as much as i know, which would fit less for your setup.
dont forget to have a sufficient magicka recovery, if you dont have any staves since sustaining magicka in prolonged fights would be harder then.