Abnninja's D&D 5e Greek Campaign Rules Q&A / Chatter RPGs PBP Pathfinder / D&D The keeper says...
Welp, what exists of 5E magic item crafting rules is in the DMG. From what I recall however, the general consensus on those rules is… don't bother. They're incomplete, and appear to be designed to discourage PCs from being crafters at all.
Can't truly say I blame them, such crafting is really tough to balance well.
If you and Abn are willing to consider alternatives, this blog has a good suggestion. Source 4z.