Page 92 of the core rulebook explains that a magic cup is every bit as difficult to make as a magic sword, and both will be expensive.
The entry to the right explains how to craft. As items should not be simple stat enhancements consider the magical abilities you may want.
P263 gives Armor examples
P268 gives Weapon examples
P265 Calyxes Single use items (Think scrolls)
P272 Magical Devices (Think wonderous items)
You need to think of what you want.
No magical creation should just outright resolve an issue.
No crafted magical item should be a purely numerical bonus.
Compare to the chart below to determine the price in silver (Weapons & Armor Below).
Decide what type of magical components would be needed to make the item you are trying to create. (This can be a vague concept, as GMs will weigh in)
Make a post in Discord, under #homebrew-ideas-suggestions with the above information, then ping the GM team about it.
Once Approved, complete missions and gather coin needed, then craft, or pay a @crafter / @enchanter to create the item.
Reference page 93, paragraph 3 in regard to possible failure & Flaws.
After completing missions for materials, the remaining craft time is simply one week.
P92 of WWN Book
Creation time for items requiring a mission to obtain ingredients are 1 week after obtaining materials.
Costs of Creating Weapons/Armor
Weapon p267 Bottom right
[+1] 12,500sp & DC 10
[+2] 25,000sp & DC +2 (12)
[+3] 50,000sp & DC +2 (14)
[Minor Power]10,000sp & DC +1
[Power useful most Combats] 25,000sp & DC +2
[Power useful every Fight] 50,000sp & DC +2
Armor/Shields p263 Bottom right
[+1] 25,000sp & DC 10 (Shields start at DC 9)
[+2] 50,000sp & DC +2 (12)
[+3] 100,000sp & DC +2 (14)
[Minor Power]10,000sp & DC +1
[Powerful or Broadly applicable] 20,000sp & DC +2
You can upgrade magical weapons. You pay the price for the upgrade from whatever you are working with...
(For example, rather than 50k to make an Armor +2 from scratch(25k*2), you only need to pay 25k to upgrade it from +1 to +2, seeing as how you already paid 50k. )
...and make the crafting check at the new, higher, DC.
(So that same Armor, going from +1 to +2 would require a DC of 12)
Failure?
If you fail the upgrade roll, you automatically gain a flaw onto the item(a 12 does not delete the item, just the upgrade), and then can choose to proceed to the failure or additional flaws as normal. Flaws are cumulative.