https://www.dndbeyond.com/magic-items/5028096-ring-of-weapon-holding

wondering if anyone has suggestions for this magic item (this is the first edition)

It is mainly meant to conceal/store/draw weapons easily, so maybe requires rouge attunement?

would that include the ammo for a bow?

I think it's fine. It's basically what hexblades do with their pact weapons. I don't think it needs limiting to Rogues. Maybe limiting it to one-handed weapons if you think it's too powerful? 

Quote from Nautical_Woods >>

would that include the ammo for a bow?

 That is a good point, maybe if you store a bow you can also store up to 20 arrows, and the quiver would equip itself automatically. Maybe the ring doesn’t transform into the weapon, but the carving detaches and grows into the weapon, then you could pull arrows out of the ring.

Quote from ShhinySilver >>

Quote from Nautical_Woods >>

would that include the ammo for a bow?

 That is a good point, maybe if you store a bow you can also store up to 20 arrows, and the quiver would equip itself automatically. Maybe the ring doesn’t transform into the weapon, but the carving detaches and grows into the weapon, then you could pull arrows out of the ring.

 That's a cool idea. That could almost be a magic item by itself. Call it "A pocketful of arrows" or something. It's just a small portable hole that you can stick a set number of arrows in and you can just reach into your pocket and pull one out when you reload.

Quote from Lostwhilefishing >>

Quote from ShhinySilver >>

Quote from Nautical_Woods >>

would that include the ammo for a bow?

 That is a good point, maybe if you store a bow you can also store up to 20 arrows, and the quiver would equip itself automatically. Maybe the ring doesn’t transform into the weapon, but the carving detaches and grows into the weapon, then you could pull arrows out of the ring.

 That's a cool idea. That could almost be a magic item by itself. Call it "A pocketful of arrows" or something. It's just a small portable hole that you can stick a set number of arrows in and you can just reach into your pocket and pull one out when you reload.

 That gives me an idea for a pocket that you can press onto something, and it will change material/color to match it, and it could be similar to a bag of holding.

I think it'd be best to just give this ring the limitation of not being compatible with any weapon that has the Ammunition property. I also think it's thematically appropriate that it also isn't compatible with weapons with the two-handed property either, but maybe that's just me. 

I also would touch up the wording of the magic item. For example, " An attuned creature wearing the ring can use a bonus action to transform the ring into the weapon chosen at attunement." sounds like the ring is able to transform into a duplicate of the chosen weapon, and not like the weapon itself is stored in an extradimensional space that the ring can swap with. There's no limit on magic items either, so this ring could give the party two instances of a Legendary Weapon. Here's how I would write it up:

"This brass ring has small veins of silver running through it.

While attuning to this ring, select one weapon with which you are proficient that lacks the Ammunition or Two-handed property, which becomes bonded to this ring. That weapon disappears and is stored in an extradimensional space connected to the ring. As a bonus action, the ring disappears from your finger and the bonded weapon appears in your hand. You can use a bonus action to return the bonded weapon to the extradimensional space, and the ring reappears on your finger . If the ring is destroyed, or if you lose your attunement to the ring, the bonded weapon will appear on the ground in the nearest unoccupied space."

Quote from TransmorpherDDS >>

I think it'd be best to just give this ring the limitation of not being compatible with any weapon that has the Ammunition property. I also think it's thematically appropriate that it also isn't compatible with weapons with the two-handed property either, but maybe that's just me. 

I also would touch up the wording of the magic item. For example, " An attuned creature wearing the ring can use a bonus action to transform the ring into the weapon chosen at attunement." sounds like the ring is able to transform into a duplicate of the chosen weapon, and not like the weapon itself is stored in an extradimensional space that the ring can swap with. There's no limit on magic items either, so this ring could give the party two instances of a Legendary Weapon. Here's how I would write it up:

"This brass ring has small veins of silver running through it.

While attuning to this ring, select one weapon with which you are proficient that lacks the Ammunition or Two-handed property, which becomes bonded to this ring. That weapon disappears and is stored in an extradimensional space connected to the ring. As a bonus action, the ring disappears from your finger and the bonded weapon appears in your hand. You can use a bonus action to return the bonded weapon to the extradimensional space, and the ring reappears on your finger . If the ring is destroyed, or if you lose your attunement to the ring, the bonded weapon will appear on the ground in the nearest unoccupied space."

 Thanks! I think this wording would work pretty well. another thing to think about is should the rarity be changed at all? It would allow you to sneak weapons into certain places, like a throne room for example.