The General Rule is you can only enchant items up to your current level...
From the Enchant Item ritual description:
The new version must be your level or lower, and the component cost equals the difference in gold piece value between the old version and the new. -Players Handbook, p.304
Exceptions exist however...
The Artificer Class is all about making items and making them better/faster/cheaper than any other class.
For example, the Master Crafter Feat:
When you use the Enchant Magic Item ritual to create a magic item, you can create a magic item of your level + your Intelligence modifier or lower.
And Mark of Making [Dragonmark]
Benefit: You have mastered the Enchant Magic Item ritual and can perform it as if you were two levels higher.
Kudos to BrianS for the dragonmark suggestion.