Depends what you wanna use I wouldn't recommend a nuke build to you at 27 mage because I believe it requires a considerable amount more skill than paw or wand mage aka tank mages. Due to the fact nuke mages rely heavily on ms which can easily screw a fight even if ure winning.
Something like 6 BoM 5 BoV is a reliable build. Go with anything after that. If you want to, you could try 6 BoM 4 BoV 4 heal 2 drain 1 fire 1 frost 1 ice 6 lightning, use as little INT as possible in your stats so if you don't need to use crystalline don't get your int to cover it's requirements. I'd recommend buying full int hween, crystalline wand and cryst dex shield if you can't afford a better one.