The classic glass cannon build means wearing light armor and using a destro staff. Stick to your storm calling tree and max that out for the damage boosting passives. Take crystal shards from dark magic and morph into crystal frags use it every time you see the purple crystals flying round your hands. Also look into the mages guild tree as the Mage light will raise spell crit and entropy will give you 20% spell damage buff for duration. The finer points of maximising the build are long to explain if your on ps4 add me NinjaMyk and I will chat with you about it