As Skywrath mage, you're going to - by default - be quite squishy and face a heap of mana problems. This build focuses around elminating those problems by buying items that build your mana pool and make you significantly more durable.
Remember: You are a long-range nuker. This build will provide you with lots of health, but that is no reason for you to get up close. Stay back and nuke from a safe distance.