This build allows Brand to take a relatively high damage since the early game. With Doran's ring, you can enjoy a nice mana regen and extra 100 health. In addition, an early Rod of Ages will allow you to rock in the early game since it would be very hard to kill you and you will always gain extra mana and health upon leveling up. Yet, it does not mean that you will suffer in late game since you will then enjoy high magic penetration due to the runes and items build. Although mana regeneration seems to be low, clarity will counter the mana problem. Regardless, you can always take a blue buff. In late game, you will continue to prosper with a high ability power, magic penetration and health. It is indeed a formidable build!

The runes build aims to enhance your sustainability and destructiveness of Brand's ability. First, Brand would enjoy a higher mana regeneration from the Seals of Clarity. Then, he would also enjoy a cool-down reduction (total of around 8% in level 18). Last but not least Brand would have a super high magic penetration that can rip your opponents apart.

This is a very common masteries build for AP carry. There are nothing much to say about it.

We can see the items are generally increasing the survivability and the destructiveness of Brand's ability. Since Brand has an extremely high damage, it is not surprising that you will get focused or ganked. That's why this build will be the best choice with high survivability and damage as well.
[*] Rod of Ages

Flash: allows you to run away when enemy gets very close. I dont recommend you to use this ability to chase enemy though since you are too slow to catch your enemy up and too slow to run away after you got the kill.

Clarity: formidable for farming and harassing since you can always have mana.

Pros
High Survivability
high magic penetration
very destructive

Cons
Slow
no spell vamp